Digital signal conversion method and digital signal conversion device

ABSTRACT

An inputted digital signal of a first format (DV video signal) is restored to a variable-length code by having its framing cancelled by a de-framing section  11 , then decoded by a variable-length decoding (VLD) section  12 , inversely quantized by an inverse quantizing (IQ) section  13 , and inversely weighted by an inverse weighting (IW) section  14 . Then, required resolution conversion in the orthogonal transform domain (frequency domain) is carried out on the inversely weighted video signal by a resolution converting section  16 . After that, the video signal having the resolution converted is weighted by a weighting (W) section  18 , then quantized by a quantizing (Q) section  19 , coded by variable-length coding by a variable-length coding (VLC) section  20 , and outputted as a digital signal of a second format (MPEG video signal).

This application is a division of U.S. application Ser. No. 11/082,022,filed Mar. 16, 2005, which is a continuation of U.S. application Ser.No. 09/341,401, filed Aug. 23, 1999, now U.S. Pat. No. 6,963,606, under35 USC 371 from International Application PCT/JP98/04986 filed Nov. 5,1998 and is entitled under 35 USC 119 to priority filing dates ofJapanese Applications P9-303132 filed Nov. 5, 1997; P9-303133 filed Nov.5, 1997; P-304623 filed Nov. 6, 1997; P-305959 filed Nov. 7, 1997;P-310721 filed Nov. 12; and P-3 14078 filed Nov. 14, 1997, the entiretythereof being incorporated herein by reference.

TECHNICAL FIELD

This invention relates to conversion processing of digital signalscompression-coded by using orthogonal transform such as discrete cosinetransform (DCT), and particularly to a digital signal conversion methodand a digital signal conversion device for converting the resolutionbetween compressed video signals of different formats.

BACKGROUND ART

Conventionally, discrete cosine transform (DCT), which is a kind oforthogonal transform coding, has been used as a coding system forefficiently compression-coding still picture data and dynamic picturedata. In handling such digital signals on which orthogonal transform hasbeen carried out, it is sometimes necessary to change the resolution ortransform base.

For example, in the case where a first orthogonally transformed digitalsignal having a resolution of 720×480 pixels as an example of homedigital video format is to be converted to a second orthogonallytransformed digital signal having a resolution of 360×240 pixels of aso-called MPEG1 format, inverse orthogonal transform is carried out onthe first signal to restore a signal on the spatial domain, and thentransform processing such as interpolation and thinning is carried outto perform orthogonal transform again, thus converting the first signalto the second signal.

In this manner, it is often the case that the orthogonally transformeddigital signal is inversely transformed once to restore the originalsignal, then processed by required transform operations, and thenorthogonally transformed again.

FIG. 28 shows an exemplary structure of a conventional digital signalprocessing device for carrying out resolution conversion as describedabove with respect to digital signals on which DCT has been carried out.

In this conventional digital signal conversion device, a video signal(hereinafter referred to as DV video signal) of a so-called “DV format”,which one format of home digital video signals, is inputted as a digitalsignal of a first format, and a video signal (hereinafter referred to asMPEG video signal) of a format in conformity to the so-called MPEG(Moving Picture Experts Group) standard is outputted as a digital signalof a second format.

A de-framing section 51 is adapted for cancelling framing of the DVvideo signal. In this de-framing section 51, the DV video signal framedin accordance with the so-called DV format is restored to avariable-length code.

A variable-length decoding (VLD) section 52 carries out variable-lengthdecoding of the video signal restored to the variable-length code by thede-framing section 51. The compressed data in the DV format iscompressed at a fixed rate so that its data quantity is reduced toapproximately ⅕ of that of the original signal, and is coded byvariable-length coding so as to improve the data compression efficiency.The variable-length decoding section 52 carries out decodingcorresponding to such variable-length coding.

An inverse quantizing (IQ) section 53 inversely quantizes the videosignal decoded by the variable-length decoding section 52.

An inverse weighting (IW) section 54 carries out inverse weighting,which is the reverse operation of weighting carried out on the videosignal inversely quantized by the inverse quantizing section 53.

The weighting operation is to reduce the value of DCT coefficient forhigher frequency components of the video signal by utilizing such acharacteristic that the human visual sense is not very acute to adistortion on the high-frequency side. Thus, the number ofhigh-frequency coefficients having a value of 0 is increased and thevariable-length coding efficiency can be improved. As a result, thequantity of arithmetic operation of the DCT transform can be reduced insome cases.

An inverse discrete cosine transform (IDCT) section 55 carries outinverse DCT (inverse discrete cosine transform) of the video signalwhich is inversely weighted by the inverse weighting section 54, andthus restores the DCT coefficient to data of the spatial domain, thatis, pixel data.

Then, a resolution converting section 56 carries out required resolutionconversion with respect to the video signal restored to the pixel databy the inverse discrete cosine transform section 55.

A discrete cosine transform (DCT) section 57 carries out discrete cosinetransform (DCT) of the video signal which is resolution-converted by theresolution converting section 56, and thus converts the video signal toan orthogonal transform coefficient (DCT coefficient) again.

A weighting (W) section 58 carries out weighting of the video signalwhich is resolution-converted and converted to the DCT coefficient. Thisweighting is the same as described above.

A quantizing (Q) section 59 quantizes the video signal weighted by theweighting section 58.

Then, a variable-length coding (VLC) section 60 carries outvariable-length coding of the video signal quantized by the quantizingsection 59 and outputs the resultant signal as an MPEG video signal.

The above-described “MPEG” is an abbreviation of the Moving PictureExperts Group of ISO/IEC JTC1/SC29 (International Organization forStandardization/International Electrotechnical Commission, JointTechnical Committee 1/Sub Committee 29). There are an ISO11172 standardas the MPEG1 standard and an IS013818 standard as the MPEG2 standard.Among these international standards, ISO11172-1 and IS013818-1 arestandardized in the multimedia multiplexing section, and ISO11172-2 andISO13818-2 are standardized in the video section, while ISO11172-3 andISO13818-3 are standardized in the audio section.

In accordance with ISO11172-2 or ISO13818-2 as the picture compressioncoding standard, an image signal is compression-coded on the picture(frame or field) basis by using the correlation of pictures in the timeor spatial direction, and the use of the correlation in the spatialdirection is realized by using DCT coding.

In addition, this orthogonal transform such as DCT is broadly employedfor various types of picture information compression coding such as JPEG(Joint Photographic Coding Experts Group).

In general, orthogonal transform enables compression coding with highcompression efficiency and excellent reproducibility by converting anoriginal signal of the time domain or spatial domain to an orthogonallytransformed domain such as the frequency domain.

The above-described “DV format” is adapted for compressing the dataquantity of digital video signals to approximately ⅕ for componentrecording onto a magnetic tape. The DV format is used for home digitalvideo devices and some of digital video devices for professional use.This DV format realizes efficient compression of video signals bycombining discrete cosine transform (DCT) and variable-length coding(VLC).

Meanwhile, a large quantity of calculation is generally required fororthogonal transform such as discrete cosine transform (DCT) and inverseorthogonal transform. Therefore, there arises a problem that resolutionconversion of video signals as described above cannot be carried outefficiently. Also, since errors are accumulated by increase in thequantity of calculation, there arises a problem of deterioration insignals.

DISCLOSURE OF THE INVENTION

In view of the foregoing status of the art, it is an object of thepresent invention to provide a digital signal conversion method and adigital signal conversion device which enable efficient conversionprocessing such as resolution conversion with less deterioration insignals by reducing the quantity of arithmetic processing of the dataquantity of signals which are processed by resolution conversion forconversion to a different format.

In order to solve the foregoing problems, a digital signal conversionmethod according to the present invention includes: a data extractionstep of extracting a part of orthogonal transform coefficients fromrespective blocks of a digital signal of a first format consisting oforthogonal transform coefficient blocks of a predetermined unit, thusconstituting partial blocks; an inverse orthogonal transform step ofcarrying out inverse orthogonal transform of the orthogonal transformcoefficients constituting each partial block, on the partial blockbasis; a partial block connection step of connecting the partial blocksprocessed by inverse orthogonal transform, thus constituting a new blockof the predetermined unit; and an orthogonal transform step oforthogonally transforming the new block on the block basis, thusgenerating a second digital signal consisting of the new orthogonaltransform block of the predetermined unit.

Also, in order to solve the foregoing problems, a digital signalconversion method according to the present invention includes: aninverse orthogonal transform step of carrying out inverse orthogonaltransform of a digital signal of a first format consisting of orthogonaltransform coefficient blocks of a predetermined unit, on the blockbasis; a block division step of dividing each block of the digitalsignal of the first format processed by inverse orthogonal transform; anorthogonal transform step of orthogonally transforming orthogonaltransform coefficients constituting each divided block, on the dividedblock basis; and a data enlargement step of interpolating eachorthogonally transformed block with an orthogonal transform coefficientof a predetermined value to constitute the predetermined unit, thusgenerating a digital signal of a second format.

Also, in order to solve the foregoing problems, a digital signalconversion device according to the present invention includes: decodingmeans for decoding a digital signal of a first format consisting oforthogonal transform coefficients of a predetermined unit; inversequantization means for inversely quantizing the decoded digital signal;resolution conversion means for extracting a part of the orthogonaltransform coefficients from adjacent blocks of orthogonal transformcoefficient blocks of the predetermined unit of the inversely quantizeddigital signal, thus constituting partial blocks, and converting theresolution; quantization means for quantizing the digital signalprocessed by resolution conversion; and coding means for coding thequantized digital signal, thus generating a digital signal of a secondformat.

Also, in order to solve the foregoing problems, a digital signalconversion device according to the present invention includes: decodingmeans for decoding a digital signal of a first format compression-codedby using orthogonal transform; inverse quantization means for inverselyquantizing the decoded digital signal; resolution conversion means forinterpolating each predetermined block of the inversely quantizeddigital signal with an orthogonal transform coefficient of apredetermined value, thus constituting a predetermined unit, andconverting the resolution; quantization means for quantizing the digitalsignal processed by resolution conversion; and coding means for codingthe quantized digital signal, thus generating a digital signal of asecond format.

Also, in order to solve the foregoing problems, a digital signalconversion method according to the present invention is adapted forconverting a digital signal of a first format consisting of orthogonaltransform coefficient blocks of a predetermined unit to a digital signalof a second format consisting of new orthogonal transform coefficientblocks of another predetermined unit. In this method, the data quantityof the digital signal of the second format is controlled by utilizingdata quantity information included in the digital signal of the firstformat.

Also, in order to solve the foregoing problems, a digital signalconversion device according to the present invention is adapted forconverting a digital signal of a first format consisting of orthogonaltransform coefficient blocks of a predetermined unit to a digital signalof a second format consisting of new orthogonal transform coefficientblocks of another predetermined unit. This device includes: decodingmeans for decoding the digital signal of the first format; inversequantization means for inversely quantizing the decoded digital signal;signal conversion means for carrying out signal processing accompanyingformat conversion of the inversely quantized digital signal;quantization means for quantizing the digital signal processed by signalprocessing; data quantity control means for controlling the dataquantity in the quantization means; and coding means for coding thedigital signal which is quantized and has its data quantity controlledby the data quantity control means, thus generating the digital signalof the second format.

Also, in order to solve the foregoing problems, a digital signalconversion method according to the present invention is adapted forconverting a digital signal of a first format to a digital signal of asecond format. This method includes: a decoding step of decoding thedigital signal of the first format; a signal conversion step ofconverting the decoded digital signal of the first format to the digitalsignal of the second format; a coding step of coding the digital signalof the second format; and a weighting processing step of collectivelycarrying out inverse weighting for the digital signal of the firstformat and weighting for the digital signal of the second format.

Also, in order to solve the foregoing problems, a digital signalconversion device according to the present invention is adapted forconverting a digital signal of a first format to a digital signal of asecond format. This device includes: decoding means for decoding thedigital signal of the first format; signal conversion means forconverting the decoded digital signal of the first format to the digitalsignal of the second format; coding means for coding the digital signalof the second format; and weighting processing means for collectivelycarrying out inverse weighting for the digital signal of the firstformat and weighting for the digital signal of the second format.

Also, in order to solve the foregoing problems, according to the presentinvention, decoding along with motion compensation is carried out on aninput information signal compression-coded along with motion detection,and signal conversion processing is carried out on this decoded signal.Then, compression coding processing is carried out on the convertedsignal along with motion detection based on motion vector information ofthe input information signal.

Also, in order to solve the foregoing problems, according to the presentinvention, partial decoding processing is carried out on an inputinformation signal processed by compression coding including predictivecoding along with motion detection and orthogonal transform coding, thusobtaining a decoded signal of the orthogonal transform domain. Then,signal conversion processing is carried out on the decoded signal of theorthogonal transform domain, and compression coding processing alongwith motion compensation prediction is carried out on the convertedsignal by using motion detection based on motion vector information ofthe input information signal.

Also, in order to solve the foregoing problems, according to the presentinvention, partial decoding processing is carried out on an inputinformation signal processed by compression coding including predictivecoding along with motion detection and orthogonal transform coding, thusobtaining a signal of the orthogonal transform domain. Then, signalconversion processing is carried out on the signal, and compressioncoding is carried out on the converted signal by adding motion vectorinformation converted on the basis of motion vector information of theinput information signal.

Also, in order to solve the foregoing problems, according to the presentinvention, a digital signal of a first format to which dynamicmode/static mode information is added in advance is decoded, and signalconversion processing is carried out on the decoded signal. Then,whether or not to carry out inter-frame differential coding for eachpredetermined block of the converted signal is discriminated inaccordance with the dynamic mode/static mode information. Coding iscarried out on the converted signal on the basis of the result ofdiscrimination, and a digital signal of a second format processed bycoding using the inter-frame difference is outputted.

Also, in order to solve the foregoing problems, according to the presentinvention, partial decoding processing is carried out on a digitalsignal of a first format, thus obtaining a signal of the orthogonaltransform domain. Signal conversion processing is carried out on thesignal of the orthogonal transform domain, and whether of not to carryout inter-frame differential coding for each predetermined block of theconverted signal is discriminated in accordance with the maximum valueof the absolute value of the inter-frame difference of the convertedsignal. The converted signal is coded on the basis of the result ofdiscrimination, and a digital signal of a second format is outputted.

Moreover, in order to solve the foregoing problems, according to thepresent invention, with respect to a digital signal of a first formatincluding an intra-frame coded signal processed by intra-frame codingand a forward predictive coded signal and a bidirectionally predictivecoded signal processed by forward and bidirectional inter-framepredictive coding along with motion detection, inverse orthogonaltransform is carried out on the intra-frame coded signal and the forwardpredictive coded signal. A motion compensation output to be added to thepartially decoded forward predictive coded signal and bidirectionallypredictive coded signal is generated on the basis of the inverseorthogonal transform output. The motion compensation output isorthogonally transformed, and the orthogonal transform output is addedto the partially decoded forward predictive coded signal andbidirectionally predictive coded signal. Compression coding is carriedout on a signal based on the addition output, and a digital signal of asecond format is outputted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a first embodiment of the presentinvention.

FIG. 2 illustrates the principle of resolution conversion in theorthogonal transform domain.

FIG. 3 illustrates the principle of resolution conversion in theorthogonal transform domain.

FIGS. 4A to 4C schematically show the state where a DV video signal isconverted to an MPEG video signal by digital signal conversion accordingto the first embodiment of the present invention.

FIG. 5 illustrates the relation between the DV format and the MPEGformat.

FIG. 6 illustrates the basic calculation procedure for resolutionconversion processing.

FIGS. 7A and 7B illustrate a “static mode” and a “dynamic mode” of theDV format.

FIG. 8 illustrates the procedure of conversion processing in the “staticmode”.

FIGS. 9A to 9C are block diagrams showing an exemplary structure of adigital signal conversion device according to a second embodiment of thepresent invention.

FIG. 10 illustrates the procedure of conversion processing inenlargement of an image.

FIG. 11 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a third embodiment of the presentinvention.

FIG. 12 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a fourth embodiment of the presentinvention.

FIG. 13 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a fifth embodiment of the presentinvention.

FIG. 14 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a sixth embodiment of the presentinvention.

FIG. 15 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a seventh embodiment of thepresent invention.

FIG. 16 is a flowchart showing the basic procedure for setting thequantizer scale for each macroblock (MB) of each frame when a DV videosignal is converted to an MPEG signal in the seventh embodiment of thepresent invention.

FIG. 17 is a flowchart showing the basic procedure for applying feedbackto a next frame by using the preset quantizer scale in the seventhembodiment of the present invention.

FIG. 18 is a block diagram showing an exemplary structure of aconventional digital signal conversion device for converting an MPEGvideo signal to a DV video signal.

FIG. 19 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to an eighth embodiment of thepresent invention.

FIG. 20 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a ninth embodiment of the presentinvention.

FIG. 21 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a tenth embodiment of the presentinvention.

FIG. 22 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a eleventh embodiment of thepresent invention.

FIG. 23 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a twelfth embodiment of thepresent invention.

FIG. 24 illustrates motion compensation and motion estimation processingin the orthogonal transform domain in the twelfth embodiment of thepresent invention, and shows the state where a macroblock B extends overa plurality of macroblocks of a reference picture.

FIG. 25 illustrates motion compensation and motion estimation processingin the orthogonal transform domain in the twelfth embodiment of thepresent invention, and shows conversion processing of a referencemacroblock.

FIG. 26 illustrates motion compensation and motion estimation processingin the orthogonal transform domain in the twelfth embodiment of thepresent invention, and shows the procedure of conversion of thereference macroblock.

FIG. 27 is a block diagram showing an exemplary structure of a digitalsignal conversion device according to a thirteenth embodiment of thepresent invention.

FIG. 28 is a block diagram showing an exemplary structure of aconventional digital signal conversion device.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference to the drawings.

First, the structure of a digital signal conversion device according tothe present invention will be described, and then a digital signalconversion method according to the present invention will be describedwith reference to the structure.

FIG. 1 shows an exemplary structure of essential portions of a digitalsignal conversion device as a first embodiment of the present invention.Although signal conversion is exemplified by resolution conversion, itis a matter of course that signal conversion is not limited toresolution conversion and that various types of signal processing suchas format conversion and filter processing can be employed.

In this digital signal conversion device, a video signal (hereinafterreferred to as DV video signal) of the above-described so-called “DVformat” is inputted as a first digital signal, and a video signal(hereinafter referred to as MPEG video signal) of a format inconformity'to the MPEG (Moving Picture Experts Group) standard isoutputted as a second digital signal.

A de-framing section 11 is adapted for cancelling framing of the DVvideo signal. In this de-framing section 11, the DV video signal framedin accordance with the predetermined format (so-called DV format) isrestored to a variable-length code.

A variable-length decoding (VLD) section 12 carries out variable-lengthdecoding of the video signal restored to the variable-length code by thede-framing section 11.

An inverse quantizing (IQ) section 13 inversely quantizes the videosignal decoded by the variable-length decoding section 12.

An inverse weighting (IW) section 14 carries out inverse weighting,which is the reverse operation of weighting carried out on the videosignal inversely quantized by the inverse quantizing section 13.

In the case where resolution conversion is carried out as an example ofsignal conversion processing, a resolution converting section 16 carriesout required resolution conversion in the orthogonal transform domain(frequency domain) with respect to the video signal inversely weightedby the inverse weighting section 14.

A weighting (W) section 18 carries out weighting of the video signalprocessed by resolution conversion.

A quantizing (Q) section 19 quantizes the video signal weighted by theweighting section 18.

Then, a variable-length coding (VLC) section 20 carries outvariable-length coding of the video signal quantized by the quantizingsection 19 and outputs the resultant signal as an MPEG video signal.

The structure of each part of the above-described digital signalconversion device according to the present invention shown in FIG. 1 canbe made similar to the structure of each part of the conventionaldigital signal conversion device shown in FIG. 28.

However, this digital signal conversion device according to the presentinvention differs from the conventional digital signal conversion devicein that an inverse discrete cosine transform (IDCT) section and adiscrete cosine transform (DCT) section are not provided before andafter the resolution converting section 16.

That is, in the conventional digital signal conversion device, theorthogonal transform coefficient of the inputted digital signal of thefirst format is inversely orthogonally transformed to be restored todata in the spatial domain (on the frequency base), and then requiredconversion operation is carried out. Therefore, orthogonal transform iscarried out again to restore the data to the orthogonal transformcoefficient.

On the contrary, in the digital signal conversion device according tothe present invention, required conversion operation of the orthogonaltransform coefficient of the inputted digital signal of the first formatis carried out in the orthogonal transform coefficient domain (frequencydomain), and inverse orthogonal transform means and orthogonal transformmeans are not provided before and after the means for carrying outconversion processing such as resolution conversion.

The principle of resolution conversion processing in the resolutionconverting section 16 will now be described with reference to FIGS. 2and 3.

In FIG. 2, an input orthogonal transform matrix generating section 1generates an inverse matrix Ts_((k)) ⁻¹ of an orthogonal transformmatrix Ts_((k)) expressing orthogonal transform that has been carriedout on an input digital signal 5 in advance, and sends the inversematrix to a transform matrix generating section 3. An output orthogonaltransform matrix generating section 2 generates an orthogonal transformmatrix Td_((L)) corresponding to an inverse transform matrix Td_((L)) ⁻¹expressing inverse orthogonal transform that is to be carried out on anoutput digital signal, and sends the orthogonal transform matrix to thetransform matrix generating section 3. The transform matrix generatingsection 3 generates a transform matrix D for carrying out conversionprocessing such as resolution conversion in the frequency domain, andsends the transform matrix to a signal converting section 4. The signalconverting section 4 converts the input digital signal 5 that has beenconverted to the frequency domain by orthogonal transform whilemaintaining the orthogonally transformed domain such as the frequencydomain, and generates an output digital signal 6.

Specifically, as shown in FIG. 3, a signal (original signal) A of theoriginal time domain (or spatial domain) is converted to the frequencydomain by using the orthogonal transform matrix Ts_((k)) to generate afrequency signal B₁ (corresponding to the input digital signal 5). Thisfrequency signal B₁ is contracted to N/L (or enlarged) by the signalconverting section 4 to generate a frequency signal B₂ (corresponding tothe output digital signal 6). This frequency signal B₂ is inverselyorthogonally transformed by using the inverse transform matrix Td_((L))⁻¹ to generate a signal C of the time domain.

In the example of FIG. 3, the one-dimensional original signal A isorthogonally transformed for each conversion block having a length of k,and m units of adjacent blocks of the resultant conversion blocks of thefrequency domain, that is, continuous frequency signals having a lengthof L (=k×m), are converted to one block having a length of N (whereN<L), that is, contracted to N/L as a whole.

In the following description, a matrix (orthogonal transform matrix) inwhich orthogonal transform base vectors e ₁, e ₂, . . . , e _(n) havinga length of n are arranged in the respective rows is expressed asT_((n)), and an inverse transform matrix thereof is expressed as T_((n))⁻¹. In this description, x denotes an x vector expression. In this case,each matrix is an n-order forward matrix. For example, a one-dimensionalDCT transform matrix T₍₈₎ where n=8 holds is expressed by the followingequation (1).

$\begin{matrix}{T_{(8)} = {\begin{pmatrix}\underset{\_}{e_{1}} \\\underset{\_}{e_{2}} \\\underset{\_}{e_{3}} \\\underset{\_}{e_{4}} \\\underset{\_}{e_{5}} \\\underset{\_}{e_{6}} \\\underset{\_}{e_{7}} \\\underset{\_}{e_{8}}\end{pmatrix} = {\frac{1}{2}\begin{pmatrix}{1/\sqrt{2}} & {1/\sqrt{2}} & {1/\sqrt{2}} & {1/\sqrt{2}} & {1/\sqrt{2}} & {1/\sqrt{2}} & {1/\sqrt{2}} & {1/\sqrt{2}} \\{\cos\left( {\pi/16} \right)} & {\cos\left( {3{\pi/16}} \right)} & {\cos\left( {5{\pi/16}} \right)} & {\cos\left( {7{\pi/16}} \right)} & {\cos\left( {9{\pi/16}} \right)} & {\cos\left( {11{\pi/16}} \right)} & {\cos\left( {13{\pi/16}} \right)} & {\cos\left( {15{\pi/16}} \right)} \\{\cos\left( {2{\pi/16}} \right)} & {\cos\left( {6{\pi/16}} \right)} & {\cos\left( {10{\pi/16}} \right)} & {\cos\left( {14{\pi/16}} \right)} & {\cos\left( {18{\pi/16}} \right)} & {\cos\left( {22{\pi/16}} \right)} & {\cos\left( {26{\pi/16}} \right)} & {\cos\left( {30{\pi/16}} \right)} \\{\cos\left( {3{\pi/16}} \right)} & {\cos\left( {9{\pi/16}} \right)} & {\cos\left( {15{\pi/16}} \right)} & {\cos\left( {21{\pi/16}} \right)} & {\cos\left( {27{\pi/16}} \right)} & {\cos\left( {33{\pi/16}} \right)} & {\cos\left( {39{\pi/16}} \right)} & {\cos\left( {45{\pi/16}} \right)} \\{\cos\left( {4{\pi/16}} \right)} & {\cos\left( {12{\pi/16}} \right)} & {\cos\left( {20{\pi/16}} \right)} & {\cos\left( {28{\pi/16}} \right)} & {\cos\left( {36{\pi/16}} \right)} & {\cos\left( {44{\pi/16}} \right)} & {\cos\left( {52{\pi/16}} \right)} & {\cos\left( {60{\pi/16}} \right)} \\{\cos\left( {5{\pi/16}} \right)} & {\cos\left( {15{\pi/16}} \right)} & {\cos\left( {25{\pi/16}} \right)} & {\cos\left( {35{\pi/16}} \right)} & {\cos\left( {45{\pi/16}} \right)} & {\cos\left( {55{\pi/16}} \right)} & {\cos\left( {65{\pi/16}} \right)} & {\cos\left( {75{\pi/16}} \right)} \\{\cos\left( {6{\pi/16}} \right)} & {\cos\left( {18{\pi/16}} \right)} & {\cos\left( {30{\pi/16}} \right)} & {\cos\left( {42{\pi/16}} \right)} & {\cos\left( {54{\pi/16}} \right)} & {\cos\left( {66{\pi/16}} \right)} & {\cos\left( {78{\pi/16}} \right)} & {\cos\left( {90{\pi/16}} \right)} \\{\cos\left( {7{\pi/16}} \right)} & {\cos\left( {21{\pi/16}} \right)} & {\cos\left( {35{\pi/16}} \right)} & {\cos\left( {49{\pi/16}} \right)} & {\cos\left( {63{\pi/16}} \right)} & {\cos\left( {77{\pi/16}} \right)} & {\cos\left( {91{\pi/16}} \right)} & {\cos\left( {105{\pi/16}} \right)}\end{pmatrix}}}} & (1)\end{matrix}$

In FIG. 3, when the size of the orthogonal transform block with respectto the input digital signal 5 that has been orthogonally transformed tothe frequency domain by using the orthogonal transform matrix Ts_((k))is k, that is, when the base length is equal to k, the input orthogonaltransform matrix generating section 1 generates the inverse orthogonaltransform matrix Ts_((k)) ⁻¹, and the output orthogonal transform matrixgenerating section 2 generates the orthogonal transform matrix Td_((L))having the base length of L (=k×m).

At this point, the inverse orthogonal transform matrix Ts_((k)) ⁻¹generated by the input orthogonal transform matrix generating section 1corresponds to inverse processing of orthogonal transform processing ingenerating the input digital signal 5, and the orthogonal transformmatrix Td_((L)) generated by the output orthogonal transform matrixgenerating section 2 corresponds to inverse processing of inverseorthogonal transform processing in decoding the output digital signalconverted by the signal converting section 4, that is, in converting thesignal to the time domain. Both these orthogonal transform matrixgenerating sections 1 and 2 can generate base vectors of arbitrarylengths.

The orthogonal transform matrix generating sections 1 and 2 may beidentical orthogonal transform matrix generating sections. In such case,the orthogonal transform matrices Ts_((k)) and Td_((L)) becomeorthogonal transform matrices of the same type, with their base lengthsalone differing from each other. The orthogonal transform matrixgenerating section exists for each of different orthogonal transformsystems.

Next, the transform matrix generating section 3 generates an L-orderforward matrix A by arranging, on the diagonal, m units of inverseorthogonal transform matrices Ts_((k)) ⁻¹ generated by the inputorthogonal transform matrix generating section 1, as expressed by thefollowing equation (2). When the base length of the output digitalsignal 6 is equal to N, the transform matrix generating section 3 takesout N units of low-frequency base vectors of the orthogonal transformmatrix Td_((L)) and generates a matrix B consisting of N rows and Lcolumns.

$\begin{matrix}{A = \begin{pmatrix}{Ts}_{(k)}^{- 1} & \; & \; & \; & \; \\\; & {Ts}_{(k)}^{- 1} & \; & 0 & \; \\\; & \; & ⋰ & \; & \; \\\; & 0 & \; & {Ts}_{(k)}^{- 1} & \; \\\; & \; & \; & \; & {Ts}_{(k)}^{- 1}\end{pmatrix}} & (2) \\{B = {\begin{pmatrix}\underset{\_}{e_{1}} \\\underset{\_}{e_{2}} \\\vdots \\\underset{\_}{e_{N}}\end{pmatrix} = \begin{pmatrix}\underset{\_}{e_{11}} & \underset{\_}{e_{12}} & \ldots & \underset{\_}{e_{{1L} - 1}} & \underset{\_}{e_{1L}} \\\underset{\_}{e_{21}} & \underset{\_}{e_{22}} & \; & \underset{\_}{e_{{2L} - 1}} & \underset{\_}{e_{2L}} \\\vdots & \; & ⋰ & \; & \vdots \\\underset{\_}{e_{N\; 1}} & \underset{\_}{e_{N\; 2}} & \ldots & \underset{\_}{e_{{NL} - 1}} & \underset{\_}{e_{NL}}\end{pmatrix}}} & (3)\end{matrix}$

In this expression, however, e ₁, e ₂, . . . , e _(N) are N units oflow-frequency base vectors when Td_((L)) is expressed by base vectors asfollows.

$\begin{matrix}{{Td}_{(L)} = {\begin{pmatrix}\underset{\_}{e_{1}} \\\underset{\_}{e_{2}} \\\underset{\_}{e_{3}} \\\vdots \\\underset{\_}{e_{L}}\end{pmatrix} = \begin{pmatrix}\underset{\_}{e_{11}} & \underset{\_}{e_{12}} & \ldots & \underset{\_}{e_{{1L} - 1}} & \underset{\_}{e_{1L}} \\\underset{\_}{e_{21}} & \underset{\_}{e_{22}} & \; & \underset{\_}{e_{{2L} - 1}} & \underset{\_}{e_{2L}} \\\underset{\_}{e_{31}} & \underset{\_}{e_{32}} & \; & \underset{\_}{e_{{3L} - 1}} & \underset{\_}{e_{3L}} \\\vdots & \; & ⋰ & \; & \vdots \\\underset{\_}{e_{L\; 1}} & \underset{\_}{e_{L\; 2}} & \ldots & \underset{\_}{e_{{LL} - 1}} & \underset{\_}{e_{LL}}\end{pmatrix}}} & (4)\end{matrix}$

Then, an equation ofD=α·B·A  (5)is calculated to generate the matrix D consisting of N rows and Lcolumns. This matrix D is a transform matrix for converting theresolution at the contraction rate (or enlargement rate) of N/L. In thisequation, α is a scalar value or vector value and is a coefficient forlevel correction.

The signal transforming section 4 of FIG. 2 collects m blocks of aninput digital signal B₁ of the frequency domain into a group, anddivides the signal into meta-blocks having a size L (where onemeta-block consisting of m blocks), as shown in FIG. 3. If the length ofthe input digital signal B₁ is not a multiple of L, the signal issupplemented and stuffed with dummy data such as 0 to make a multiple ofL. The meta-blocks thus generated are expressed by Mi (where i=0, 1, 2,. . . ).

The above-described principle of resolution conversion processing isdescribed in detail in PCT/JP98/02653 filed by the present Assignee on16 Jun. 1998.

A digital signal conversion method of the first embodiment will now bedescribed with reference to the structure of the above-described digitalsignal conversion device.

FIGS. 4A to 4C schematically show processing in converting a DV videosignal to an MPEG video signal by digital signal conversion of theembodiment of the present invention. This processing is carried outmainly by the resolution converting section 16 in the digital signalprocessing device of the embodiment of the present invention shown inFIG. 1.

In the following description, a one-dimensional DCT coefficient block isused as an example. However, processing for two-dimensional DCTcoefficients is similarly carried out.

First, four DCT coefficients on the low-frequency side are taken outfrom each of adjacent blocks (i) and (i+1), each consisting of eight DCTcoefficients of the digital signal of the first format, as shown in FIG.4A. That is, from among eight DCT coefficients a0, a1, a2, a3, . . . ,a7 of the block (i), only the four DCT coefficients a0, a1, a2 and a3 onthe low-frequency side are taken out, and a partial block having thenumber of DCT coefficients reduced to ½ is produced. Similarly, fromamong eight DCT coefficients b0, b1, b2, b3, . . . , b7 of the block(i+1), only the four DCT coefficients b0, b1, b2 and b3 on thelow-frequency side are taken out, and a partial block having the numberof DCT coefficients reduced to ½ is produced. The operation of takingout the DCT coefficient on the low-frequency side is based on such acharacteristic that the energy is concentrated to low frequencies of DCand AC when the video signal is frequency-converted.

Then, 4-point inverse discrete cosine transform (4-point IDCT) iscarried out on each partial block consisting of four DCT coefficients,thus obtaining contracted pixel data. These pixel data are expressed aspixel data p0, p1, p2, p3 and pixel data p4, p5, p6, p7 in FIG. 4B.

Next, the partial blocks, each consisting of the contracted pixel dataprocessed by inverse discrete cosine transform, are coupled to generatea block having the same size as the original block. That is, the pixeldata p0, p1, p2, p3 and the pixel data p4, p5, p6, p7 are coupled togenerate a new block consisting of eight pixel data.

Then, 8-point discrete cosine transform (8-point DCT) is carried out onthe new block consisting of eight pixel data, thus generating one block(j) consisting of eight DCT coefficients c0, c1, c2, c3, . . . , c7, asshown in FIG. 4C.

Through the procedures as described above, a video signal can beconverted to a video signal of a format of different resolution bythinning the number of orthogonal transform coefficients (DCTcoefficients) per predetermined block unit to half. When the number ofDCT coefficients is to be thinned to ¼, the above-described processingis carried out continuously twice.

The above-described resolution conversion processing can be applied to,for example, conversion from the DV format to the MPEG1 format.

The relation between the DV format and the MPEG format and formatconversion between these formats will now be described with reference toFIG. 5.

Specifically, in the case of a video signal in conformity to the NTSCsystem as shown in FIG. 5, a video signal of the DV format is acompressed video signal having a resolution of 720×480 pixels and aratio of the sampling frequency of a luminance signal to the samplingfrequencies of two color-difference signals equal to 4:1:1. A videosignal of the MPEG1 format is a compressed video signal having aresolution of 360×240 pixels and a ratio of the sampling frequency of aluminance signal to the sampling frequencies of two color-differencesignals equal to 4:2:0. Therefore, in this case, the number of DCTcoefficients in the horizontal and vertical directions of the luminance(Y) signal maybe reduced to ½ and the number of DCT coefficients in thevertical direction of the color-difference (C) signal may be reduced to¼ by the above-described resolution conversion processing according tothe present invention.

The ratio of 4:2:0 represents the value of either an odd line or an evenline since the odd line and the even line alternately take the values of4:2:0 and 4:0:2.

On the other hand, in the case of a video signal in conformity to thePAL system, a video signal of the DV format is a compressed video signalhaving a resolution of 720×576 pixels and a ratio of the samplingfrequency of a luminance signal to the sampling frequencies of twocolor-difference signals equal to 4:2:0. A video signal of the MPEG1format is a compressed video signal having a resolution of 360×288pixels and a ratio of the sampling frequency of a luminance signal tothe sampling frequencies of two color-difference signals equal to 4:2:0.Therefore, in this case, the number of DCT coefficients in thehorizontal and vertical directions of the Y signal may be reduced to ½and the number of DCT coefficients in the horizontal and verticaldirections of the C signal may be reduced to ½ by the above-describedresolution conversion processing according to the present invention.

The above-described resolution conversion processing can similarlyapplied to conversion from the DV format to the MPEG2 format.

In the case of a video signal in conformity to the NTSC system, a videosignal of the MPEG2 format is a compressed video signal having aresolution of 720×480 pixels and a ratio of the sampling frequency of aluminance signal to the sampling frequencies of two color-differencesignals equal to 4:2:0. Therefore, in this case, the number of DCTcoefficients in the vertical direction of the C signal may be reduced to½ and the number of DCT coefficients in the horizontal direction of theC signal may be doubled, without carrying out conversion processing ofthe Y signal. The method for this enlargement will be described later.

In the case of a video signal in conformity to the PAL system, a videosignal of the MPEG2 format is a compressed video signal having aresolution of 720×576 pixels and a ratio of the sampling frequency of aluminance signal to the sampling frequencies of two color-differencesignals equal to 4:2:0. Therefore, in this case, conversion processingneed not be carried out with respect to either the Y signal or the Csignal.

FIG. 6 shows the basic calculation procedure for the above-describedresolution conversion processing.

Specifically, the block consisting of eight DCT coefficients, producedby connecting four DCT coefficients a0, a1, a2, a3 and fourDCT-coefficients b0, b1, b2, b3 taken out from the two adjacent blocksof the inputted digital signal of the first format, is multiplied by an(8×8) matrix including two inverse discrete cosine transform matrices(IDCT4) on the diagonal, each being provided as a (4×4) matrix, andhaving 0 as other components.

The product thereof is further multiplied by a discrete cosine transformmatrix (DCT8) provided as an (8×8) matrix, and a new block. consistingof eight DCT coefficients c0, c1, c2, c3, . . . , c7 is generated.

In the digital signal conversion method according to the presentinvention, since resolution conversion processing is carried out in theDCT domain (frequency domain), inverse DCT before resolution conversionand DCT after resolution conversion are not necessary. In addition, byfinding the product of the (8×8) matrix including the two (4×4) inversediscrete cosine transform matrices (IDCT4) on the diagonal and the (8×8)discrete cosine transform matrix as a transform matrix D in advance, thequantity of arithmetic operation can be effectively reduced.

The processing for converting the DV video signal as the digital signalof the first format to the MPEG1 video signal as the digital signal ofthe second format will be described further in detail.

The DV format has a “static mode” and a “dynamic mode” which areswitched in accordance with the result of motion detection of pictures.For example, these modes are discriminated by motion detection beforeDCT of each (8×8) matrix in a video segment, and DCT is carried out ineither one mode in accordance with the result of discrimination. Variousmethods for motion detection may be considered. Specifically, a methodof comparing the sum of absolute values of inter-field differences witha predetermined threshold value may be employed.

The “static mode” is a basic mode of the DV format, in which (8×8) DCTis carried out on (8×8) pixels in a block.

The (8×8)-block is constituted by one DC component and 63 AC components.

The “dynamic mode” is used for avoiding such a case that if DCT iscarried out when an object is moving, the compression efficiency islowered by dispersion of energy due to interlace scanning. In thisdynamic mode, an (8×8)-block is divided into a (4×8)-block of a firstfield and a (4×8)-block of a second field, and (4×8) DCT is carried outon the pixel data of each (4×8)-block. Thus, increase in high-frequencycomponents in the vertical direction is restrained and the compressionrate can be prevented from being lowered.

Each (4×8)-block as described above is constituted by one DC componentand 31 AC components.

Thus, in the DV format, the block structure differs between the staticmode and the dynamic mode. Therefore, in order to enable similarprocessing for the subsequent processing, an (8×8)-block is constitutedwith respect to the block of the dynamic mode by finding the sum anddifference of the coefficients of the same order of each block after DCTof each (4×8)-block. By such processing, the block of the dynamic modecan be regarded as being constituted by one DC component and 63 ACcomponents, similarly to the block of the static mode.

Meanwhile, in converting the video signal of the DV format to the videosignal of the MPEG1 format, it is necessary to separate only one fieldsince the MPEG1 format only handles a video signal of 30 frames/sec andhas no concept of field.

FIG. 7A schematically shows processing for separating fields inconverting DCT coefficients in accordance with the “dynamic mode (2×4×8DCT mode)” of the DV format to DCT coefficients of the MPEG1 format.

An upper-half (4×8)-block 31 a of a DCT coefficient block 31 of (8×8) isthe sum (A+B) of coefficients of a first field and coefficients of asecond field, and a lower-half (4×8)-block 31 b of the DCT coefficientblock 31 of (8×8) is the difference (A−B) of the coefficients of the twofields.

Therefore, by adding the upper-half (4×8)-block 31 a and the lower-half(4×8)-block 31 b of the DCT coefficient block 31 of (8×8) and thendividing the sum by 2, a (4×8)-block 35 a consisting of the DCTcoefficients of the first field (A) can be obtained. Similarly, bysubtracting the lower-half (4×8)-block 31 b from the (4×8)-block 31 aand then dividing the difference by 2, a (4×8)-block 35 b consisting ofthe discrete cosine coefficients of the second field (B) can beobtained. That is, by this processing, an (8×8)-block 35 having theseparated fields can be obtained.

Then, the above-described resolution conversion processing is carriedout on the DCT coefficients of one of these fields, for example, thefirst field.

FIG. 7B schematically shows the processing for separating fields in the“static mode (8×8 DCT mode)”.

In a DCT coefficient block 32 of (8×8), DCT coefficients of a firstfield (A) and DCT coefficients of a second field (B) are mixed. Thus, itis necessary to carry out conversion processing for obtaining a(4×8)-block 35 a consisting of the first field (A) and a (4×8)-block 35b consisting of the second field (B) similarly through subtractionbetween the (4×8)-block 31 a and the (4×8)-block 31 b, by using fieldseparation processing which will be described hereinafter.

FIG. 8 shows the procedure of field separation processing in the “staticmode”.

First, an input consisting of eight DCT coefficients d0, d1, d2, d3, . .. , d7 is multiplied by an 8th-order inverse discrete cosine transformmatrix (IDCT8), thus restoring pixel data.

Next, the data is multiplied by an (8×8) matrix for field separation,thus dividing the (8×8)-block into a first field on the upper side and asecond field on the lower side, each being a (4×8)-block.

Then, the data is further multiplied by an (8×8)-block including twodiscrete cosine transform matrices (DCT4) on the diagonal, each beingprovided as a (4×4)-matrix.

Thus, eight DCT coefficients consisting of four DCT coefficient e0, e1,e2, e3 of the first field and four DCT coefficients f0, f1, f2, f3 ofthe second field are obtained.

Then, the above-described resolution conversion processing is carriedout on the DCT coefficients of one of these fields, for example, thefirst field.

In the digital signal conversion method according to the presentinvention, since resolution conversion is carried out in the DCT domain(frequency domain), inverse DCT before resolution conversion and DCTafter resolution conversion are not necessary. In addition, by findingthe product of the (8×8) matrix including the two (4×4) inverse discretecosine transform matrices (IDCT4) on the diagonal and the (8×8) discretecosine transform matrix in advance, the quantity of calculation can beeffectively reduced.

The above-described resolution conversion is for contracting an image.Hereinafter, resolution conversion processing for enlarging an imagewill be described as a second embodiment.

FIGS. 9A to 9C schematically show the state where a DV video signal isconverted to an MPEG2 video signal by the digital signal conversionmethod according to the present invention.

Also in the following description, one-dimensional DCT coefficients areused. However, similar processing can be carried out on two-dimensionalDCT coefficients.

First, 8-point inverse discrete cosine transform (8-point IDCT) iscarried out on a block (u) consisting of eight orthogonal coefficients(DCT coefficients g0 to g7) shown in FIG. 9A, thus restoring eight pixeldata (h0 to h7).

Next, the block consisting of eight pixel data is divided into twoparts, thus generating two partial blocks each consisting of four pixeldata.

Then, 4-point DCT is carried out on the two partial blocks eachconsisting of four DCT coefficients, thus generating two partial blocks(i0 to i3 and j0 to j3) each consisting of four DCT coefficients.

Then, as shown in FIG. 9C, the high-frequency side of each of the twopartial blocks, each consisting of four pixel data, is stuffed with 0 asfour DCT coefficients. Thus, a block (v) and a block (v+1) eachconsisting of eight DCT coefficients are generated.

In accordance with the above-described procedure, resolution conversionbetween compressed video signals of different formats is carried out inthe orthogonal transform domain.

FIG. 10 shows the procedure of conversion processing in this case.

First, an input consisting of eight DCT coefficients g0, g1, g2, g3, . .. , g7 is multiplied by an 8th-order inverse discrete cosine transform(IDCT) matrix, thus restoring eight pixel data.

Next, the block consisting of eight pixel data is divided into twoparts, thus generating two partial blocks each consisting of four pixeldata.

Then, each of the two partial blocks, each consisting of four DCTcoefficients, is multiplied by a (4×8)-matrix including a 4-pointdiscrete cosine transform matrix provided as a (4×4)-matrix on the upperside and a 0-matrix provided as a (4×4) matrix on the lower side. Thus,two partial blocks (i0 to i7 and j0 to j7) including eight DCTcoefficients are generated.

By such processing, two blocks of DCT coefficients are obtained from oneblock. Therefore, the resolution can be enlarged in the frequencydomain.

In the case of the NTSC system, in order to convert the DV format to theMPEG2 format, it is not necessary to carry out horizontal and verticalconversion of the luminance signal Y, but it is necessary to enlarge thecolor-difference signal C to a double in the horizontal direction andcontract the color-difference signal C to ½ in the vertical direction,as shown in FIG. 5. Therefore, the above-described enlargementprocessing is used for resolution conversion of the color-differencesignal C in the horizontal direction in converting the DV format to theMPEG2 format.

FIG. 11 shows an exemplary structure of essential portions of a digitalsignal conversion device according to a third embodiment of the presentinvention. The same parts of the structure as those of the firstembodiment are denoted by the same reference numerals. The differencefrom the structure of FIG. 1 is that the weighting section 18 and theinverse weighting section 14 are collectively provided as a weightingprocessing section 21.

Specifically, the weighting processing (IW*W) section 21 collectivelycarries out inverse weighting, which is reverse operation of weightingperformed on a DV video signal as an inputted digital signal of a firstformat, and weighting for an MPEG video signal as an outputted digitalsignal of a second format.

With such a structure, since inverse weighting processing for theinputted video signal of the first format and weighting processing forthe outputted video signal of the second format can be collectivelycarried out, the quantity of calculation can be reduced in comparisonwith the case where inverse weighting processing and weightingprocessing are separately carried out.

In the digital signal conversion device of the third embodiment shown inFIG. 11, the weighting processing section 21 is provided on thesubsequent stage to the resolution converting section 16. However, theweighting processing section may be provided on the stage preceding theresolution converting section 16.

FIG. 12 shows a digital signal conversion device according to a fourthembodiment of the present invention, in which a weighting processingsection 22 is provided on the stage preceding the resolution convertingsection 16. The parts of the structure of this digital signal conversiondevice shown in FIG. 12 can be made similar to the respective parts ofthe digital signal conversion device of FIG. 11.

The weighting processing for collectively carrying out inverse weightingof the digital signal of the first format and weighting of the seconddigital signal and the above-described weighting processing can becarried out before or after orthogonal transform such as discrete cosinetransform (DCT). This is because arithmetic operations therefor arelinear operations.

A digital signal conversion method and device according to a fifthembodiment of the present invention will now be described with referenceto FIG. 13.

This digital video signal conversion device has a decoding section 8 fordecoding the DV video signal, a resolution converting section 16 forcarrying out resolution conversion processing for format conversion ofthe decoding output from the decoding section 8, a discriminatingsection 7 for discriminating whether or not to carry out forwardinter-frame differential coding for each predetermined block unit of theconversion output from the resolution converting section 16 inaccordance with the dynamic mode/static mode information, and a codingsection 9 for coding the conversion output from the resolutionconverting section 16 on the basis of the result of discrimination fromthe discriminating section 7 and outputting the MPEG video signal, asshown in FIG. 13.

In the following description, the digital video signal conversion deviceconstituted by these parts is employed. As a matter of course, therespective parts carry out processing of each step of the digital signalconversion method according to the present invention.

In the DV video signal inputted to this digital video signal conversiondevice, a mode flag (for example, one bit) as information indicating thestatic mode/dynamic mode is added to each DCT block in advance.

In this digital video signal conversion device, the discriminatingsection 7 discriminates whether or not to carry out forward inter-framedifferential coding for each predetermined block unit of the conversionoutput from the resolution converting section 16 on the basis of themode flag. This operation will be later described in detail.

A de-framing section 11 extracts the mode flag indicating the staticmode/dynamic mode and supplies the mode flag to the discriminatingsection 7.

A de-shuffling section 15 cancels shuffling which is carried out touniform the information quantity in a video segment as a unit for lengthfixation on the DV coding side.

The discriminating section 7 includes an adder 27 and an I (I-picture)/P(P-picture) discriminating and determining section 28. The adder 27 addsto the resolution conversion output a reference DCT coefficient as anegative DCT coefficient stored in a frame memory (FM) section 24 aswill be later described. The I/P discriminating and determining section28 to which the addition output from the adder 27 is supplied is alsosupplied with the mode flag indicating the static mode/dynamic mode fromthe de-framing section 11.

The operation of the I/P discriminating and determining section 28 willnow be described in detail. The conversion output from the resolutionconverting section 16 has 8×8 DCT coefficients as a unit. Four DCTcoefficient blocks each having 8×8 DCT coefficients are allocated to theluminance signal, and two DCT coefficient blocks are allocated to thecolor-difference signal, thus constituting one predetermined block fromsix DCT coefficient blocks in total. This predetermined block isreferred to as a macroblock.

Meanwhile, a P-picture assumes that the difference from the previousframe is simply taken. In the case of a still image, the informationquantity is reduced as the difference is taken. However, in the case ofa dynamic image, the information quantity is increased as the differenceis taken. Therefore, if it is discriminated that the image is dynamicfrom the mode flag indicating the static mode/dynamic mode, themacroblock is left as an I-picture so as not to increase the informationquantity. If it is discriminated that the image is static, efficientcoding can be carried out by taking the difference to make a P-picture.

The I/P discriminating and determining section 28 uses an I-picture forthe macroblock when all the mode flags sent from the de-framing sectionwith respect to the six DCT coefficient blocks indicate the dynamicmode. On the other hand, when the flag indicating the dynamic mode canbe detected only in one of the six DCT coefficient blocks, the I/Pdiscriminating and determining section 28 uses a P-picture for themacroblock.

If the flag of the dynamic mode is added to four or more DCT coefficientblocks of the six DCT coefficient blocks, an I-picture may be used forthe macroblock. Also, when the flag indicating the static mode is addedto all the six DCT coefficient blocks, a P-picture may be used for themacroblock.

The DCT coefficients on the macroblock basis determined as anI/P-picture by the I/P discriminating and determining section 28 aresupplied to the coding section 9.

The coding section 9 has a weighting (W) section 18, a quantizing (Q)section 19, an inverse quantizing (IQ) section 26, an inverse weighting(IW) section 25, a FM section 24, a variable-length coding (VLC) section20, a buffer memory 23, and a rate control section 29.

The weighting (W) section 18 carries out weighting on the DCTcoefficient as the conversion output supplied from the convertingsection 16 through the discriminating section 7.

The quantizing (Q) section 19 quantizes the DCT coefficient weighted bythe weighting (W) section 18. Then, the variable-length coding (VLC)section 20 carries out variable-length coding of the DCT coefficientquantized by the quantizing section 19 and supplies MPEG coded data tothe buffer memory 23.

The buffer memory 23 fixes the transfer rate of the MPEG coded data andoutputs the MPEG coded data as a bit stream. The rate control section 29controls increase and decrease in the quantity of generated informationof the quantizing (Q) section 19, that is, the quantization step, inaccordance with change information such as increase and decrease in thebuffer capacity of the buffer memory 23.

The inverse quantizing (IQ) section 26 inversely quantizes the quantizedDCT coefficient from the quantizing (Q) section 19 and supplies theinversely quantized DCT coefficient to the inverse weighting (IW)section 25. The inverse weighting (IW) section 25 carries out inverseweighting, which is reverse operation of weighting, on the DCTcoefficient from the inverse quantizing (IQ) section 26. The DCTcoefficient processed by inverse weighting by the inverse weighting (IW)section 25 is stored in the FM section 24 as a reference DCTcoefficient.

As described above, in the digital video signal conversion device shownin FIG. 13, the discriminating section 7 discriminates an I-picture or aP-picture for each macroblock by using the I/P discriminating anddetermining section 28 in accordance with the mode flag indicating thedynamic mode/static mode sent from the de-framing section 11. Therefore,the DV signal originally consisting of an I-picture alone can beconverted to an MPEG picture using an I-picture or a P-picture, and suchan advantage as improvement in the compression rate as a feature of theMPEG video signal can be utilized.

A digital signal conversion method and device according to a sixthembodiment of the present invention will now be described.

The digital video signal conversion device according to the sixthembodiment is a digital video signal conversion device in which thediscriminating section 7 shown in FIG. 13 is replaced by adiscriminating section 30 shown in FIG. 14.

Specifically, the digital video signal conversion device has a decodingsection 8 for carrying out partial decoding processing on the DV signaland obtaining a signal of the orthogonal transform domain such as a DCTcoefficient, a converting section 16 for carrying out signal conversionprocessing for format conversion with respect to the DCT coefficientfrom the decoding section 8, a discriminating section 30 fordiscriminating whether or not to carry out forward inter-framedifferential coding for each predetermined block unit of the conversionoutput from the converting section 16 in accordance with the maximumvalue of the absolute value of the inter-frame difference of theconversion output, and a coding section 9 for coding the conversionoutput from the converting section 16 on the basis of the result ofdiscrimination from the discriminating section 30 and outputting theMPEG video signal.

The discriminating section 30 refers to the maximum value of theabsolute value of an AC coefficient at the time when the differencebetween the converted DCT coefficient as the conversion output from theconverting section 16 and a reference DCT coefficient from a FM section24 is taken, and compares this maximum value with a predeterminedthreshold value. The discriminating section 30 allocates an I/P-pictureto each macroblock on the basis of the result of comparison.

The discriminating section 30 has a difference calculating section 31, amaximum value detecting section 32, a comparing section 33, and an I/Pdetermining section 35.

The difference calculating section 31 calculates the difference betweenthe converted DCT coefficient from the converting section 16 and thereference DCT coefficient from the FM section 24. The differentialoutput from the difference calculating section 31 is supplied to themaximum value detecting section 32 and is also supplied to the I/Pdetermining section 35.

The maximum value detecting section 32 detects the maximum value of theabsolute value of the AC coefficient of the differential output.Basically, when a large quantity of information is converted to DCTcoefficients, the AC coefficient becomes large. On the other hand, whena small quantity of information is converted to DCT coefficients, the ACcoefficient becomes small.

The comparing section 33 compares the maximum value of the absolutevalue from the maximum value detecting section 32 with a predeterminedthreshold value supplied from a terminal 34. As this predeterminedthreshold value is appropriately selected, the quantity of informationconverted to the DCT coefficients can be discriminated in accordancewith the maximum value of the absolute value of the AC coefficient.

The I/P determining section 35 discriminates whether the difference ofthe DCT coefficients from the difference calculating section 31, thatis, the difference in the information quantity, is large or small byusing the result of comparison from the comparing section 33. When it isdiscriminated that the difference is large, the I/P determining section35 allocates an I-picture to a macroblock consisting of the convertedDCT coefficient block from the converting section 16. When it isdiscriminated that the difference is small, the I/P determining section35 allocates a P-picture to a macroblock from the difference calculatingsection 31.

That is, if the absolute value of the maximum value is greater than thethreshold value, it is discriminated that the information quantity ofthe difference is large and an I-picture is employed as the macroblock.On the other hand, if the absolute value of the maximum value is smallerthan the threshold value, it is discriminated that the informationquantity of the difference is small and a P-picture is employed as themacroblock.

Thus, the digital video signal conversion device according to the sixthembodiment is capable of converting a DV signal originally consisting ofan I-picture to an MPEG picture using an I-picture or a P-picture, andcan utilize the advantage of improvement in the compression rate as afeature of MPEG signal video signals.

In the digital video signal conversion device shown in FIGS. 13 and 14,a DV signal and an MPEG1 video signal in conformity to the NTSC systemare used as the input and output, respectively. However, this digitalvideo signal conversion device can also be applied to each signal of thePAL system.

The above-described resolution conversion processing can be similarlyapplied to conversion from the DV format to the MPEG2 format.

As the resolution conversion processing carried out by the convertingsection 16, resolution conversion for contraction is mainly describedabove. However, enlargement is also possible. Specifically, in general,the resolution can be enlarged at an arbitrary magnification by adding ahigh-frequency component to an input digital signal of the frequencydomain.

When an MPEG2 video signal is applied to a digital broadcasting service,the signal is classified in accordance with the profile (function)/level(resolution). Enlargement of the resolution can be applied to, forexample, the case where a video signal of the main profile/high level(MP@HL) used for a digital HDTV in the United States is converted to theDV signal.

The processing of the sixth embodiment may also be carried out bysoftware means.

A digital signal conversion method and device according to a seventhembodiment of the present invention will now be described with referenceto FIG. 15. The same parts of the structure as those of theabove-described embodiment are denoted by the same reference numerals.

A rate control section 40 controls the data quantity in a quantizingsection 19 on the basis of a quantizer number (Q_NO) and a class number(Class) from a de-framing section 11.

FIG. 16 shows the basic procedure for setting the quantizer scale foreach macroblock (MB) of each frame in converting a DV video signal to anMPEG video signal by the digital signal conversion method of the seventhembodiment.

First, at step S1, a quantizer number (Q_NO) and a class number (Class)are obtained for each macroblock. This quantizer number (Q_NO) isexpressed by a value of 0 to 15 and is common to all the six DCT blocksin the macroblock. The class number (Class) is expressed by a value of 0to 3 and is provided for each of the six DCT blocks.

Next, at step S2, a quantization parameter (q_param) is calculated foreach DCT block in accordance with the following procedure.Quantization table q_table[4]={9, 6, 3, 0}Quantization parameter q_param=Q _(—) NO+q_table[class]

Specifically, the quantization table has four kinds of values (9, 6, 3,0), which correspond to the class numbers 0, 1, 2, 3, respectively. Forexample, when the class number is 2 and the quantizer number 8, thequantization table value 3 corresponding to the class number 2 and thequantizer number 8 are added to produce a quantization parameter of 11.

Next, at step S3, the average of the quantization parameters (q_param)of the six DCT blocks in the macroblock is calculated.

Then, at step S4, the quantizer scale (quantizer_scale) of the MPEGmacroblock is found in accordance with the following procedure, and theprocessing ends.

$\begin{matrix}{{{Quantization}\mspace{14mu}{table}\mspace{14mu}{{q\_ table}\lbrack 25\rbrack}} = \left\{ {32,16,16,16,16,8,8,8,8,4,} \right.} \\{4,4,2,2,2,2,2,2,2,2,} \\\left. {2,2,2,2} \right\}\end{matrix}$ quantizer_scale = q_table[q_param]

Specifically, the quantization table has 25 kinds of values (32 to 2),which correspond to the quantization parameters calculated in theabove-described manner.

-   The quantization table corresponding to the quantization parameter    value of 0 is 32.-   The quantization table corresponding to the quantization parameter    value of 1 is 16.-   The quantization table corresponding to the quantization parameter    value of 5 is 8.    For example, when the average value of the quantization parameters    found in the above-described manner is 10, the value of 4    corresponding to the quantization parameter value of 10 becomes the    quantizer scale value. Through this procedure, the MPEG quantizer    scale (quantizer_scale) depending on the target rate is calculated    on the basis of the quantization parameter (q_param) for each    macroblock within each frame. The corresponding relation between the    class number and the quantization table and the relation between the    quantization parameter and the quantizer scale are experientially    found.

In the digital signal conversion device of the present invention shownin FIG. 15, the above-described processing is carried out by the ratecontrol section 40 on the basis of the quantization number (Q_NO) andthe class number (Class) sent from the de-framing section 11.

FIG. 17 shows the basic procedure for applying feedback to the nextframe by using the quantizer scale set in accordance with theabove-described procedure.

First, at step S11, the number of target bits per frame at the bit rateset in accordance with the above-described procedure is set.

Next, at step S12, the total number of generated bits per frame isintegrated.

Next, at step S13, the difference (diff) between the number of targetbits and the total number of generated bits is calculated.

Then, at step S14, the quantizer scale is adjusted on the basis of theresult of calculation.

The calculation at each step is expressed as follows.diff=cont*diff(cont: constant)q_param=q_param±f(diff)quantizer_scale=q_table[q_param]

Specifically, normalization is carried out by multiplying thedifferential value diff found at step S13 by the constant cont. Thenormalized differential value is multiplied by an experientially foundfunction and added to or subtracted from the quantization parameter. Theresultant value is used as the quantization parameter. The valuecorresponding to this quantization parameter value is selected from thequantization table having 25 kinds of values and is used as thequantizer scale for the next frame.

Through the foregoing procedure, feedback between frames is carried outby calculating the new quantizer scale (quantizer_scale) on the basis ofthe adjusted quantization parameter (q_param) and using the newquantizer scale for the next frame.

A digital signal conversion method and a digital signal conversiondevice according to an eighth embodiment of the present invention willnow be described. Although the DV format is converted to the MPEG formatin the foregoing embodiments, the MPEG format is converted to the DVformat in the following embodiment.

With reference to FIG. 18, a conventional device for converting the MPEGformat to the DV format will be described first.

The digital video signal conversion device shown in FIG. 18 isconstituted by an MPEG decoder 70 for decoding MPEG2 video data and a DVencoder 80 for outputting DV video data.

In the MPEG decoder 70, a parser 71, which is supplied with a bit streamof the MPEG2 video data, detects the header of a bit stream of aquantized DCT coefficient framed in accordance with the MPEG2 format andsupplies the quantized DCT coefficient coded by variable-length codingto a variable-length decoding (VLD) section 72. Also, the parser 71extracts a motion vector (mv) and supplies the extracted motion vectorto a motion compensation (MC) section 77.

The variable-length decoding (VLD) section 72 carries outvariable-length decoding of the quantized DCT coefficient coded byvariable-length coding and supplies the variable-length decoding resultto an inverse quantizing (IQ) section 73.

The inverse quantizing section 73 carries out inverse quantization bymultiplying the quantized DCT coefficient decoded by the variable-lengthdecoding section 72 by the quantization step used on the coding side.Thus, the inverse quantizing section 73 obtains the DCT coefficient andsupplies the DCT coefficient to an inverse discrete cosine transform(IDCT) section 74.

The inverse discrete cosine transform section 74 performs inverse DCT onthe DCT coefficient from the inverse quantizing section 73, thusrestoring the DCT coefficient to data of the spatial domain, that is,pixel data. Specifically, by inverse DCT, pixel values (luminance Y andcolor difference Cr, Cb) are calculated for each block consisting of 8×8pixels. In the case of an I-picture, the pixel value is the actual pixelvalue itself. However, in the case of a P-picture and a B-picture, thepixel value is the differential value between the corresponding pixelvalues.

The motion compensation section 77 generates a motion compensationoutput by using picture information stored in two frame memories FM of aframe memory (FM) section 76 and the motion vector mv extracted by theparser 71, and supplies this motion compensation output to an adder 75.

The adder 75 adds the motion compensation output to the differentialvalue from the inverse discrete cosine transform section 74 and suppliesdecoded picture data to a discrete cosine transform (DCT) section 81 ofthe DV encoder 80 and the frame memory section 76.

In the DV encoder 80, the discrete cosine transform section 81 performsDCT processing on the decoded picture data to again convert the decodedpicture data to the data of the orthogonal transform domain, that is,the DCT coefficient, and supplies the DCT coefficient to a quantizing(Q) section 82.

The quantizing section 82 quantizes the DCT coefficient by using amatrix table in consideration of the visual characteristics and suppliesthe quantization result as an I-picture of the DV format to avariable-length coding (VLC) section 83.

The variable-length coding section 83 compresses the I-picture of the DVformat by carrying out variable-length coding processing and suppliesthe compressed I-picture to a framing section 84.

The framing section 84 frames the DV format data on whichvariable-length coding processing is performed and outputs a bit streamof the DV video data.

Meanwhile, orthogonal transform such as discrete cosine transform (DCT)and inverse transform thereof generally require a large quantity ofcalculation and therefore raise a problem that format conversion ofvideo data as described above cannot be carried out efficiently. Sinceerrors are accumulated along with the increase in the calculationquantity, there is also a problem that the signal is deteriorated.

Thus, a digital video signal conversion device according to the eighthembodiment to solve these problems will be described with reference toFIG. 19.

In the digital signal conversion device shown in FIG. 19, an MPEG videosignal in conformity to the MPEG format as described above is inputtedas a first digital signal, and a DV signal is outputted as a seconddigital signal.

A parser 111 extracts motion information- of the image such as themotion vector mv and the quantizer scale with reference to the header ofthe MPEG video signal as the digital signal of the first format.

The motion vector mv is sent to a motion compensation (MC) section 115,where motion compensation is carried out. The quantizer scale(quantizer_scale) is sent to an evaluating section 123, which will bedescribed later.

A variable-length decoding (VLD) section 112 carries out variable-lengthdecoding on the bit stream of the MPEG video signal from which necessaryinformation is extracted by the parser 111.

An inverse quantizing (IQ) section 113 inversely quantizes the MPEGvideo signal decoded by the variable-length decoding section 112.

Then, the MPEG video signal inversely quantized by the inversequantizing section 113 is inputted to an adder 125. To this adder 125,the result of motion compensation for the motion vector mv from theparser 111 is also inputted from the motion compensation section 115.

The output from the adder 125 is sent to a signal converting section116, which will be described later, and is also inputted to the motioncompensation section 115 through a frame memory 114. The signalconverting section 116 performs required signal conversion processingsuch as resolution conversion in the orthogonal transform domain(frequency domain) on the video signal inputted through the adder 125.

The video signal on which required signal conversion processing isperformed by the signal converting section 116 is shuffled by ashuffling section 117 and is then sent to a buffer 118 and a classifyingsection 122.

The video signal sent to the buffer 118 is sent to a quantizing (Q)section 119 and is quantized by this quantizing section 119. Then, thevideo signal is variable-length coded by a variable-length coding (VLC)section 120. In addition, the video signal is framed by a framingsection 121 and outputted as a bit stream of the DV video signal.

On the other hand, the classifying section 122 classifies the videosignal shuffled by the shuffling section 117 and sends the result ofclassification as class information to the evaluating section 123.

The evaluating section 123 determines the quantization number at thequantizing section 119 on the basis of the class information from theclassifying section 122 and the quantizer scale (quantizer_scale) fromthe parser 111.

With such a structure, since the data quantity of the DV video signaloutputted as the video signal of the second format can be determined onthe basis of the data quantity information included in the MPEG videosignal inputted as the video signal of the first format, processing fordetermining the data quantity of the video signal of the second formatgenerated by signal conversion can be simplified.

The above-described seventh and eighth embodiments can also be appliedto the case where one of the digital signal of the first format and thedigital signal of the second format is an MPEG1 video signal while theother is an MPEG2 video signal.

A digital signal conversion method and a digital signal conversiondevice according to a ninth embodiment of the present invention will nowbe described with reference to FIG. 20.

The digital signal conversion device is a device for converting MPEGvideo data conforming to the MPEG2 format to DV video data conforming tothe DV format. It is assumed that these data are data of the PAL system.

In the case where the video signal is a signal of the PAL system, thesignals conforming to the MPEG2 format and the DV format have aresolution of 720×576 pixels and a ratio of the sampling frequency of aluminance signal to the sampling frequencies of two color-differencesignals equal to 4:2:0. Therefore, resolution conversion processing neednot be carried out with respect to either the Y signal or the C signal.

In FIG. 20, an MPEG decoder 100 has a parser 111, a variable-lengthdecoding (VLD) section 112, an inverse quantizing (IQ) section 113, anadder 125, an inverse discrete cosine transform (IDCT) section 131, aframe memory (FM) section 132, a motion compensation (MC) section 115,and a discrete cosine transform (DCT) section 130. The frame memory (FM)section 132 is so constituted as to be used as two predictive memories.

As will be later described in detail, the inverse discrete cosinetransform section 131 carries out inverse discrete cosine transformprocessing on an I-picture and a P-picture partially decoded by thevariable-length decoding section 112 and the inverse quantizing section113. The motion compensation section 115 generates a motion compensationoutput on the basis of the inverse discrete cosine transform output. Thediscrete cosine transform section 130 carries out discrete cosinetransform on the motion compensation output. The adder 125 adds themotion compensation output from the discrete cosine transform section130 to a P-picture and a B-picture partially decoded by thevariable-length decoding section 112 and the inverse quantizing section113.

The overall operation will be described hereinafter. First, the parser111 restores the quantized DCT coefficient framed in conformity to theMPEG2 format to a variable-length code with reference to the header ofthe MPEG2 video data inputted as a bit stream, and supplies thevariable-length code to the variable-length decoding section 112. Also,the parser 111 extracts the motion vector (mv) and supplies theextracted motion vector to the motion compensation section 115.

The variable-length decoding section 112 carries out variable-lengthdecoding of the quantized DCT coefficient restored to thevariable-length code, and supplies the variable-length decoding resultto the inverse quantizing section 113.

The inverse quantizing section 113 carries out inverse quantizationprocessing by multiplying the quantized DCT coefficient decoded by thevariable-length decoding section 112 by the quantization step used onthe coding side. The inverse quantizing section 113 thus obtains the DCTcoefficient and supplies the DCT coefficient to the adder 125. The DCTcoefficient obtained by the variable-length decoding section 112 and theinverse quantizing section 113 is supplied to the adder 125 as an outputwhich will not be restored to pixel data by inverse discrete cosinetransform, that is, as partially decoded data.

The adder 125 is also supplied with the motion compensation output fromthe motion compensation section 115, which is orthogonally transformedby the discrete cosine transform section 130. Then, the adder 125 addsthe motion compensation output to the partially decoded data in theorthogonal transform domain. The adder 125 supplies the addition outputto a DV encoder 110 and also to the inverse discrete cosine transformsection 131.

The inverse discrete cosine transform section 131 performs inversediscrete cosine transform processing on an I-picture or a P-picturewithin the addition output, thus generating data of the spatial domain.This data of the spatial domain is reference picture data used formotion compensation. The reference picture data for motion compensationis stored in the frame memory section 132.

The motion compensation section 115 generates the motion compensationoutput by using the reference picture data stored in the frame memorysection 132 and the motion vector mv extracted by the parser 111, andsupplies the motion compensation output to the discrete cosine transformsection 130.

The discrete cosine transform section 130 restores the motioncompensation output processed in the spatial domain to the orthogonaltransform domain as described above and then supplies the motioncompensation output to the adder 125.

The adder 125 adds the DCT coefficient of the motion compensation outputfrom the discrete cosine transform section 130 to the DCT coefficient ofthe differential signal of the partially decoded P- and B-pictures fromthe inverse quantizing section 113. Then, the addition output from theadder 125 is supplied as partially decoded data in the orthogonaltransform domain to the DV encoder 110 and the inverse discrete cosinetransform section 131.

Since the partially decoded I-picture from the inverse quantizingsection 113 is an intra-frame coded image signal, motion compensationaddition processing is not necessary. The partially decoded I-picture issupplied as it is to the inverse discrete cosine transform section 131and is also supplied to the DV encoder 110.

The DV encoder 110 includes a quantizing (Q) section 141, avariable-length coding (VLC) section 142, and a framing section 143.

The quantizing section 141 quantizes the decoded output, that is, theDCT coefficient, of the I-picture, P-picture and B-picture in theorthogonal transform domain from the MPEG decoder 100, and supplies thequantized DCT coefficient to the variable-length coding section 142.

The variable-length coding section 142 carries out variable-lengthcoding processing of the quantized DCT coefficient and supplies thecoded data to the framing section 143. The framing section 143 framesthe compression-coded data from the variable-length coding section 142and outputs a bit stream of DV video data.

In this manner, when the MPEG2 video data to be converted is anI-picture, the MPEG decoder 100 causes the variable-length decodingsection 112 and the inverse quantizing section 113 to partially decodethe MPEG2 video data to the orthogonal transform domain, and the DVencoder 110 causes the quantizing section 141 and the variable-lengthcoding section 142 to partially code the video data. At the same time,the MPEG decoder 100 causes the inverse discrete cosine transformsection 131 to perform inverse discrete cosine transform on theI-picture and stores the resultant I-picture into the frame memorysection 132 as a reference picture for the P/B-picture.

On the other hand, when the MPEG2 video data to be converted is aP-picture or a B-picture, only the processing for generating the motioncompensation output is carried out in the spatial domain by using theinverse discrete cosine transform section 131, and the processing forconstituting the frame in addition to the differential signal as theP-picture or B-picture partially decoded by the variable-length decodingsection 112 and the inverse quantizing section 113 is carried out in thediscrete cosine transform domain by using the discrete cosine transformsection 130, as described above. After that, partial encoding is carriedout by the DV encoder 110.

Particularly, in the case of the P-picture, a macroblock at a positionindicated by the motion vector mv is taken out from the I-pictureprocessed by inverse discrete cosine transform by the inverse discretecosine transform section 131, by motion compensation processing by themotion compensation section 115. Discrete cosine transform processing isperformed on the macroblock by the discrete cosine transform section 130and is added to the DCT coefficient of the P-picture as a differentialsignal in the discrete cosine transform domain by the adder 125. Thisprocessing is based on that the result of discrete cosine transformperformed on the addition result in the spatial domain is equivalent tothe result of addition of data processed by discrete cosine transform.This result is partially encoded by the DV encoder 110. At the sametime, as a reference for the next B-picture, inverse discrete cosinetransform is performed on the addition output from the adder 125 by theinverse discrete cosine transform section 131 and the resultant data isstored in the frame memory section 132.

In the case of the B-picture, a macroblock at a position indicated bythe motion vector mv is taken out from the P-picture which is processedby inverse discrete cosine transform by the inverse discrete cosinetransform section 131. Then, discrete cosine transform is carried out onthe macroblock by the discrete cosine transform section 130, and the DCTcoefficient of the B-picture as a differential signal is added theretoin the discrete cosine transform domain. In the bidirectional case,macroblocks from two reference frames are taken out and the averagethereof is used.

The result is partially encoded by the DV encoder 110. Since theB-picture does not become a reference frame, inverse discrete cosinetransform need not be carried out by the inverse discrete cosinetransform section 131.

While both inverse discrete cosine transform (IDCT) and discrete cosinetransform (DCT) processing are conventionally required to decode anI-picture, the digital video signal conversion device according to theabove-described ninth embodiment only requires IDCT for reference.

To decode a P-picture, DCT and IDCT processing for reference arenecessary. However, while both DCT and IDCT are conventionally requiredto decode a B-picture, the digital video signal conversion deviceaccording to the embodiment only requires DCT and needs no IDCT.

In the case of typical MPEG2 data having the number of GOPs N=15 and theforward predictive picture spacing M=3, one I-picture, four P-pictures,and 10 B-pictures are included. On the assumption that the calculationquantity of DCT and that of IDCT are substantially equal, when weightingis omitted, the MPEG2 data per 15 frames is expressed by

2 × DCT × (1/15) + 2 × DCT × (4/15) + 2 × DCT × (10/15) = 2 × DCTin the case of the conventional technique, and is expressed by

1 × DCT × (1/15) + 2 × DCT × (4/15) + 1 × DCT × (10/15) = 1.2666 × DCTin the case of the digital video signal conversion device shown in FIG.20. Thus, the calculation quantity can be significantly reduced. DCT inthese equations represents the calculation quantity.

That is, in the digital video signal conversion device shown in FIG. 20,the quantity of data calculation processing for format conversion fromMPEG2 video data to DV video data can be significantly reduced.

A digital video signal conversion device according to a tenth embodimentof the present invention will now be described with reference to FIG.21.

In this tenth embodiment, too, a digital video signal conversion devicefor converting MPEG video data conforming to the MPEG2 format to DVvideo data conforming to the DV format is employed. However, it isassumed that the MPEG2 video data is a compressed video signal of a highresolution, for example, 1440×1080 pixels.

For example, when an MPEG2 video signal is applied to a digitalbroadcasting service, the signal is classified in accordance with theprofile (function)/level (resolution). A video signal of the mainprofile/high level (MP@HL) used for a digital HDTV in the United Stateshas a high resolution, as described above, and this signal is convertedto the DV video data.

Therefore, the digital video signal conversion device shown in FIG. 21has such a structure that a signal converting section 140 for carryingout the above-described conversion processing is provided between theMPEG decoder 100 and the DV encoder 110 of FIG. 20.

This signal converting section 140 carries out resolution conversionprocessing on the DCT coefficient in the DCT transform domain from theMPEG decoder, by using a transform matrix generated on the basis of aninverse orthogonal transform matrix corresponding to the orthogonaltransform matrix used for DCT coding performed on the MPEG coded dataand an orthogonal transform matrix corresponding to the inverseorthogonal transform matrix used for IDCT coding for obtaining a signalconversion output signal in the time domain.

The DCT coefficient as a resolution conversion output from this signalconverting section 140 is supplied to the DV encoder 110.

The DV encoder 110 carries out quantization and variable-length codingon the DCT coefficient as the resolution conversion output, then framesthe DCT coefficient, and outputs a bit stream of DV video data.

Thus, in this digital video signal conversion device, the video signalof the main profile/high level (MP@HL) within the MPEG video signal isresolution-converted by the signal converting section 140 and then codedby the DV encoder to generate the DV video data.

Similarly to the digital video signal conversion device of FIG. 20, withrespect to an I-picture, the digital video signal conversion device ofthis tenth embodiment only requires IDCT for reference, whereas bothIDCT and DCT processing are conventionally required.

With respect to a P-picture, DCT and IDCT for reference are carried outas in the conventional technique. With respect to a B-picture, thisdigital video signal conversion device only requires DCT and needs noIDCT, while both DCT and IDCT are conventionally required.

That is, in the digital video signal conversion device of FIG. 21, too,the quantity of data calculation processing for format conversion fromMPEG2 video data of a high resolution to DV video data can besignificantly reduced.

As the resolution conversion processing carried out by the signalconverting section 140, resolution conversion for contraction is mainlydescribed. However, enlargement is also possible. Specifically, ingeneral, the resolution can be enlarged at an arbitrary magnification byadding a high-frequency component to an input digital signal of thefrequency domain. For example, format conversion from MPEG1 video datato the DV video data is carried out.

The above-described processing may also be carried out by means ofsoftware.

Meanwhile, in the above-described compression system of the MPEG formator the DV format, a hybrid compression coding method using orthogonaltransform coding in combination with predictive coding is employed inorder to efficiently compression-code still image data or dynamic imagedata.

When orthogonal transform and predictive coding along with motioncompensation are carried out again after resolution conversionprocessing is carried out on an input information signal which iscompression-coded by the hybrid compression coding method, the motionvector must be estimated at the step of carrying out re-predictivecoding processing.

If predictive coding is carried out again with perfectly the sameresolution without carrying out resolution conversion processing, themotion vector at the time of predictive coding may be used. However, ifthe resolution is converted, the conversion distortion is changed.Therefore, the motion vector used at the re-predictive coding step isalso changed.

Thus, the motion vector needs to be estimated at the re-predictivecoding step. However, the quantity of arithmetic processing is requiredfor estimation of the motion vector.

To eliminate this problem, a digital signal conversion device accordingto an eleventh embodiment is used. In the digital signal conversionmethod and device according to the eleventh embodiment, an inputinformation signal which is compression-coded by hybrid compressioncoding using orthogonal transform coding in combination with predictivecoding is processed by signal conversion processing such as resolutionconversion in the time domain or the orthogonal transform domain andthen restored to the orthogonal transform domain for re-compressioncoding, or compression-coded in the orthogonal transform domain.

The above-described hybrid compression coding is exemplified by H.261and H.263 recommended by ITU-T (International TelecommunicationUnion—Telecommunication Standardization Section), and MPEG and DV codingstandards.

The H.261 standard is an image coding standard for a low bit rate and isdeveloped mainly for teleconference and video phone through ISDN. TheH.263 standard is an improved version of H.261 for the GSTN video phonesystem.

The eleventh embodiment will now be described with reference to FIG. 22.In the digital video signal conversion device of the eleventhembodiment, MPEG coded data conforming to the MPEG format is inputtedand processed by resolution conversion processing as signal conversionprocessing, and the resolution-converted MPEG coded data is outputted.

This digital video signal conversion device has a decoding section 210for carrying out decoding using motion compensation MC with respect to abit stream of MPEG coded data which is compression-coded along withmotion vector (mv) detection, a resolution converting section 160 forperforming resolution conversion processing on the decoding output fromthe decoding section 210, and a coding section 220 for performingcompression coding processing along with motion detection based on themotion vector mv added to the MPEG coded data, on the conversion outputimage from the resolution converting section 160, and outputting a bitstream of video coded data which is resolution-converted, as shown inFIG. 22.

The digital video signal conversion device constituted by these partswill be described hereinafter. It is a matter of course that eachconstituent part carries out processing of each step of the digitalsignal conversion method according to the present invention.

The decoding section 210 includes a variable-length decoding (VLD)section 112, an inverse quantizing (IQ) section 113, an inverse discretecosine transform (IDCT) section 150, an adder 151, a motion compensation(MC) section 152, and a frame memory (FM) section 153. The FM section153 is constituted by two frame memories FM used as predictive memories.

The VLD section 112 decodes the MPEG coded data, that is, coded dataobtained by variable-length coding of the motion vector and thequantized DCT coefficient as additional information, in accordance withvariable-length coding, and extracts the motion vector mv. The IQsection 113 carries out inverse quantization processing by multiplyingthe quantized DCT coefficient decoded by the VLD section 112 by thequantization step used on the coding side, thus obtaining the DCTcoefficient.

The IDCT section 150 performs inverse DCT on the DCT coefficient fromthe IQ section 113, thus restoring the DCT coefficient to data of thespatial domain, that is, pixel data. Specifically, by inverse DCT, therespective pixel values (luminance Y and color-difference Cr, Cb) arecalculated for each block consisting of 8×8 pixels. In the case of anI-picture, the pixel value is the actual pixel value itself However, inthe case of a P-picture and a B-picture, the pixel value is thedifferential value between the corresponding pixel values.

The MC section 152 performs motion compensation processing on the imageinformation stored in the two frame memories of the FM section 153 byusing the motion vector mv extracted by the VLD section 112, andsupplies the motion compensation output to the adder 151.

The adder 151 adds the motion compensation output from the MC section152 to the differential value from the IDCT section 150, thus outputtinga decoded image signal. The resolution converting section 160 carriesout required resolution conversion processing on the decoded imagesignal. The conversion output from the resolution converting section 160is supplied to the coding section 220.

The coding section 220 includes a scale converting section 171, a motionestimation (ME) section 172, an adder 173, a DCT section 175, a ratecontrol section 183, a quantizing (Q) section 176, a variable-lengthcoding (VLC) section 177, a buffer memory 178, an IQ section 179, anIDCT section 180, an adder 181, an FM section 182, and an MC section174.

The scale converting section 171 carries out scale conversion of themotion vector mv extracted by the VLD section 112 in accordance with theresolution conversion rate used by the resolution converting section160. For example, if the resolution conversion rate used by theresolution converting section 160 is ½, the motion vector mv isconverted to the scale of ½.

The ME section 172 searches a narrow range of the conversion output fromthe resolution converting section 160 by using scale conversioninformation from the scale converting section 171, thus estimating theoptimum motion vector at the converted resolution.

The motion vector estimated by the ME section 172 is used at the time ofmotion compensation carried out by the MC section 174. The conversionoutput image from the resolution converting section 160 used forestimation of the motion vector by the ME section 172 is supplied to theadder 173.

The adder 173 calculates the difference between a reference picturewhich will be later described and the conversion output from theresolution converting section 160, and supplies the difference to theDCT section 175.

The DCT section 175 carries out discrete cosine transform of thedifference between the reference picture obtained by motion compensationby the MC section 174 and the conversion output picture, by using ablock size of 8×8. With respect to an I-picture, since intra-framecoding is carried out, DCT arithmetic operation is directly carried outwithout calculating the difference between frames.

The quantizing (Q) section 176 quantizes the DCT coefficient from theDCT section 175 by using a matrix table in consideration of the visualcharacteristics. The VLC section 177 compresses the quantized DCTcoefficient from the Q section 176 by using variable-length coding.

The buffer memory 178 is a memory for maintaining a constant transferrate of the coded data which is compressed by variable-length coding bythe VLC section 177. From this buffer memory 178, theresolution-converted video coded data is outputted as a bit stream at aconstant transfer rate.

The rate control section 183 controls the increase/decrease in thequantity of generated information in the Q section 176, that is, thequantization step, in accordance with the change information about theincrease/decrease in the buffer capacity of the buffer memory 178.

The IQ section 179 constitutes a local decoding section together withthe IDCT section 180. The IQ section 179 inversely quantizes thequantized DCT coefficient from the Q section 176 and supplies the DCTcoefficient to the IDCT section 180. The IDCT section 180 carries outinverse DCT of the DCT coefficient from the IQ section 179 to restorepixel data and supplies the pixel data to the adder 181.

The adder 181 adds the motion compensation output from the MC section174 to the pixel data as the inverse DCT output from the IDCT section180. The image information as the addition output from the adder 181 issupplied to the FM section 182. The image information stored in the FMsection 182 is processed by motion compensation by the MC section 174.

The MC section 174 carries out motion compensation on the imageinformation stored in the FM section 182 by using the optimum motionvector estimated by the ME section 172, and supplies the motioncompensation output as a reference picture to the adder 173.

The adder 173 calculates the difference between the conversion outputpicture from the resolution converting section 160 and the referencepicture, and supplies the difference to the DCT section 175, asdescribed above.

The DCT section 175, the Q section 176, the VLC section 177 and thebuffer memory 178 operate as described above. Ultimately, theresolution-converted video coded data is outputted as a bit stream at aconstant transfer rate from this digital video signal conversion device.

In this digital video signal conversion device, when the motion vectoris estimated by the ME section 172 of the coding section 220, the motionvector appended to the macroblock of the original compressed videosignal is converted in scale by the scale converting section 171 inaccordance with the resolution conversion rate in the resolutionconverting section 160, and the narrow range of the conversion outputpicture from the resolution converting section 160 is searched on thebasis of the scale conversion information from the scale convertingsection 171 so as to estimate the motion vector for motion compensation,instead of estimating the motion vector in the absence of anyinformation. Thus, since the calculation quantity in the ME section 172can be significantly reduced, miniaturization of the device andreduction in the conversion processing time can be realized.

A twelfth embodiment will now be described. In this embodiment, too, adigital video signal conversion device for performing resolutionconversion processing on an MPEG video signal and outputting aresolution-converted video signal is employed.

This digital video signal conversion device has a decoding section 211for obtaining decoded data of the orthogonal transform domain bycarrying out only predictive decoding processing using MC with respectto MPEG coded data on which the above-described hybrid coding isperformed, a resolution converting section 260 for performing resolutionconversion processing on the decoded data of the orthogonal transformdomain from the decoding section 211, and a coding section 221 forperforming compression coding processing along with motion compensationprediction on the conversion output from the resolution convertingsection 260 by using motion detection based on motion vector informationof the MPEG coded data, as shown in FIG. 23.

The digital video signal conversion device constituted by these partswill be described hereinafter. It is a matter of course that eachconstituent part carries out processing of each step of the digitalsignal conversion method according to the present invention.

In this digital video signal conversion device, compared with the deviceshown in FIG. 22, the IDCT section 150 is not necessary in the decodingsection 210, and the DCT section 175 and the IDCT section 180 are notnecessary in the coding section 220. That is, in this digital videosignal conversion device, resolution conversion processing carried outon the decoded data of the DCT domain and the conversion output thereofis coded.

Orthogonal transform such as DCT and inverse orthogonal transformgenerally require a large calculation quantity. Therefore, resolutionconversion as described above may not be carried out efficiently. Also,since errors are accumulated along with the increase in the calculationquantity, the signal might be deteriorated.

Thus, in the digital video signal conversion device of FIG. 23, the IDCTsection 150, the DCT section 174 and the IDCT section 180 of FIG. 22 areeliminated and the function of the resolution converting section 160 ischanged.

Also, in order to calculate activity which will be later described fromthe conversion DCT coefficient from the resolution converting section160 in the DCT domain and estimate the motion vector by using theactivity, an activity calculating section 200 is used in place of thescale converting section 171 of FIG. 22.

The resolution converting section 260 shown in FIG. 23 is supplied withan addition output (DCT coefficient) which is obtained by an adder 251by adding a motion compensation output from an MC section 252 to a DCTcoefficient obtained by an IQ section 213 by inversely quantizing aquantized DCT coefficient decoded by a VLD section 212.

This resolution converting section 260 carries out resolution conversionprocessing on the DCT coefficient of the DCT transform domain from thedecoding section 211, by using a transform matrix generated on the basisof an inverse orthogonal transform matrix corresponding to theorthogonal transform matrix used for DCT coding performed on the MPEGcoded data and an orthogonal transform matrix corresponding to theinverse orthogonal transform matrix used for IDCT coding for obtaining asignal conversion output signal in the time domain.

The DCT coefficient as the resolution conversion output from theresolution converting section 260 is supplied to the activitycalculating section 200. The activity calculating section 200 calculatesthe spatial activity for each macroblock from the luminance component ofthe DCT coefficient from the resolution converting section 260.Specifically, the feature of the image is calculated by using themaximum value of the AC value of the DCT coefficient. For example, theexistence of fewer high-frequency components indicates a flat image.

An ME section 272 estimates the optimum motion vector at the convertedresolution on the basis of the activity calculated by the activitycalculating section 200. Specifically, the ME section 272 converts themotion vector mv extracted by the VLD 212 on the basis of the activitycalculated by the activity calculating section 200 so as to estimate themotion vector mv, and supplies the estimated motion vector mv to an MCsection 274. The ME section 272 estimates the motion vector in theorthogonal transform domain. This motion estimation in the orthogonaltransform domain will be described later.

The resolution-converted DCT coefficient from the resolution convertingsection 260 is supplied to an adder 273 through the activity calculatingsection 200 and the ME section 272.

The adder 273 calculates the difference between a reference DCTcoefficient which will be later described and the converted DCTcoefficient from the resolution converting section 260, and supplies thedifference to a quantizing (Q) section 276.

The Q section 276 quantizes the differential value (DCT coefficient) andsupplies the quantized DCT coefficient to a VLC section 277 and an IQsection 279.

A rate control section 283 controls the increase/decrease in thequantity of generated information in the Q section 276, that is, thequantization step, in accordance with the activity information from theactivity calculating section 200 and the change information about theincrease/decrease in the buffer capacity of a buffer memory 278.

The VLC section 277 compression-codes the quantized DCT coefficient fromthe Q section 276 by using variable-length coding and supplies thecompressed DCT coefficient to the buffer memory 278. The buffer memory278 maintains a constant transfer rate of the coded data which iscompressed by variable-length coding by the VLC section 277, and outputsthe resolution-converted video coded data as a bit stream at a constanttransfer rate.

The IQ section 279 inversely quantizes the quantized DCT coefficientfrom the Q section 276 and supplies the DCT coefficient to the adder281. The adder 281 adds the motion compensation output from the MCsection 274 to the DCT coefficient as the inverse quantization outputfrom the IQ section 279. The DCT coefficient information as the additionoutput from the adder 281 is supplied to the FM section 282. The DCTcoefficient information stored in the FM section 282 is processed bymotion compensation by the MC section 274.

The MC section 274 carries out motion compensation on the DCTcoefficient information stored in the FM section 282 by using theoptimum motion vector estimated by the ME section 272, and supplies themotion compensation output as a reference DCT coefficient to the adder281.

The adder 273 calculates the difference between the converted DCTcoefficient from the resolution converting section 260 and the referenceDCT coefficient, and supplies the difference to the Q section 276, asdescribed above.

The Q section 276, the VLC section 277 and the buffer memory 278 operateas described above. Ultimately, the resolution-converted video codeddata is outputted at a constant transfer rate from this digital videosignal conversion device.

The MC section 274 carries out motion compensation in the orthogonaltransform domain similarly to the ME section 272, by using the optimummotion vector estimated by the ME section 272 and the reference DCTcoefficient stored in the FM section 282.

Motion estimation and motion compensation in the orthogonal transformdomain will now be described with reference to FIGS. 24 to 26. In FIG.24, solid lines represent macroblocks of a picture A to be compressedand dotted lines represent macroblocks of a reference picture B. Whenthe picture A to be compressed and the reference picture B are caused tooverlap each other by using a motion vector as shown in FIG. 24, theboundaries of macroblocks may not coincide. In the case of FIG. 24, amacroblock B′ to be compressed now extends partially on four macroblocksB₁, B₂, B₃ and B₄ of the reference picture B. Therefore, no macroblockof the reference picture B corresponds to the macroblock B′ one-on-one,and the DCT coefficient of the reference picture B at a position of themacroblock B′ cannot be obtained. Thus, it is necessary to obtain theDCT coefficient of the reference picture B of the portion where themacroblock B′ is located, by converting the DCT coefficient of the fourmacroblocks of the reference picture B over which the macroblock B′partially extends.

FIG. 25 schematically shows the procedure of this conversion processing.Since the lower left part of the macroblock B₁ of the reference pictureB overlaps the upper right part of the macroblock B′, a macroblock B ₃is generated by converting the DCT coefficient of the macroblock B₁ aswill be later described. Similarly, since the lower right part of themacroblock B₂ of the reference picture B overlaps the upper left part ofthe macroblock B′, a macroblock B₂₄ is generated by converting the DCTcoefficient of the macroblock B₂ as will be later described. Similarprocessing is carried out on the macroblocks B₃ and B₄, thus generatingmacroblocks B₃₁ and B₄₂. By combining the four macroblocks B₁₃, B₂₄, B₃₁and B₄₂ thus generated, the DCT coefficient of the reference picture Bof the portion where the macroblock B′ is located can be obtained.

In short, this processing can be expressed by the following equations(6) and (7).B′=B ₁₃ +B ₂₄ +B ₃₁ +B ₄₂  (6)DCT(B′)=DCT(B ₁₃)+DCT(B ₂₄)+DCT(B ₃₁)+DCT(B ₄₂)  (7)

Conversion of the DCT coefficient of the macroblock will now bedescribed with reference to FIG. 26. FIG. 26 shows a mathematical modelfor finding the partial macroblock B₄₂ by calculation from the originalblock B₄ or the like in the spatial domain. Specifically, B₄ on theupper left side is extracted, interpolated with 0, and shifted to thelower right side. That is, B₄₂ obtained by calculation of the followingequation (8) from the block B₄ is shown.

$\begin{matrix}{{B_{42} = {H_{1} \times B_{4} \times H_{2}}}{{H_{1} = \begin{bmatrix}0 & 0 \\I_{h} & 0\end{bmatrix}},{H_{2} = \begin{bmatrix}0 & I_{W} \\0 & 0\end{bmatrix}}}} & (8)\end{matrix}$

In this equation, Ih and Iw are identification codes of a matrix havinga size of h×h consisting of h-columns and h-rows and a matrix having asize of w×w consisting of w-columns and w-rows extracted from the blockB₄. As shown in FIG. 26, with respect to a pre-matrix H₁ which issynthesized with B₄ first, the first h-column is extracted and convertedto the bottom. With respect to H2 which is synthesized with B₄ later,the first w-row is extracted and converted to the right side.

On the basis of the equation (8), the DCT coefficient of B₄₂ can becalculated directly from the DCT coefficient of B₄ in accordance withthe following equation (9).DCT(B ₄₂)=DCT(H ₁)×DCT(B ₄)×DCT(H ₂)  (9)

This equation is applied to all the subblocks and the total iscalculated. Thus, the DCT coefficient of the new block B′ can beobtained directly from the DCT coefficients of the original blocks B₁ toB₄, as expressed by the following equation (10).

$\begin{matrix}{{{DCT}\left( B^{\prime} \right)} = {\sum\limits_{i = 1}^{4}{{{DCT}\left( H_{i\; 1} \right)} \times {{DCT}\left( B_{i} \right)} \times {{DCT}\left( H_{i\; 2} \right)}}}} & (10)\end{matrix}$

The DCT coefficients of H_(i1) and H_(i2) may be calculated and storedin a memory in advance so as to constitute a table memory. In thismanner, motion estimation and motion compensation can be carried outeven in the orthogonal transform domain.

Then, in the coding section 221, when the motion vector is estimated bythe ME section 272, the motion vector appended to the macroblock of theoriginal compressed video signal is estimated by searching a narrowrange on the basis of the activity calculated by the activitycalculating section 200 from the conversion output of the resolutionconverting section 260, instead of estimating the motion vector in theabsence of any information.

As described above, in the decoding section 211 of the digital videosignal conversion device of this embodiment, predictive decodingprocessing along with motion compensation is carried out on the MPEGcoded data on which hybrid coding including predictive coding along withmotion detection and orthogonal transform coding is performed, that is,inverse quantization is carried out after variable-length decoding.Then, motion compensation is carried out to obtain decoded data whichremains in the DCT domain, and resolution conversion is performed on thedecoded data of the DCT domain. Therefore, resolution conversion can bedirectly carried out in the orthogonally transformed domain and decoding(inverse orthogonal transform) to the time domain or spatial domain isnot necessary. Thus, the calculation is simplified and conversion ofhigh quality with less computational errors can be carried out.Moreover, in the coding section 221, when the motion vector is estimatedby the ME section 272, the motion vector appended to the macroblock ofthe original compressed video signal is estimated by searching a narrowrange on the basis of the activity calculated from the resolutionconversion output, instead of estimating the motion vector in theabsence of any information. Therefore, as the calculation quantity ofthe ME section 272 can be significantly reduced, miniaturization of thedevice and reduction in the conversion processing time can be realized.

A thirteenth embodiment will now be described. In this embodiment, too,a digital video signal conversion device for performing signalconversion processing such as resolution conversion processing on MPEGcoded data and outputting video coded data is employed.

This digital video signal conversion device has a decoding section 340for obtaining data of the orthogonal transform domain by carrying outpartial decoding processing on MPEG coded data on which theabove-described hybrid coding is performed, a converting section 343 forperforming resolution conversion processing on the data of theorthogonal transform domain from the decoding section 340, and a codingsection 350 for adding a motion vector based on motion vectorinformation of the MPEG coded data and performing compression codingprocessing on the conversion output from the converting section 343, asshown in FIG. 27.

The decoding section 340 includes a VLD section 341 and an IQ section342. These VLD section 341 and IQ section 342 have the structuressimilar to those of the VLD section 112 and the IQ section 113 of FIG.21, respectively, and operate similarly. The characteristic of thisdecoding section 340 is that motion compensation is not carried out.

Specifically, with respect to a P-picture and a B-picture, resolutionconversion is carried out by the converting section 343 with respect tothe DCT coefficient as differential information, without carrying outmotion compensation. The converted DCT coefficient obtained throughresolution conversion is quantized by a Q section 345 which iscontrolled in rate by a rate control section 348. The DCT coefficient isvariable-length coded by a VLC section 346 and then outputted at aconstant rate from a buffer memory 347.

In this case, a motion vector converting section 344 of the codingsection 350 rescales the motion vector mv extracted by the VLD section341 in accordance with the resolution conversion rate and supplies therescaled motion vector to the VLC section 346.

The VLC section 346 adds the rescaled motion vector mv to the quantizedDCT coefficient from the Q section 345 and carries out variable-lengthcoding processing. The VLC section 346 then supplies the coded data tothe buffer memory 347.

As described above, in the digital video signal conversion device shownin FIG. 27, since motion compensation is not carried out in the decodingsection 340 and the coding section 350, the calculation can besimplified and the burden on the hardware can be reduced.

In the above-described digital video signal conversion devices, rateconversion may be carried out. In short, the digital video signalconversion devices may be applied to conversion of the transfer ratefrom 4 Mbps to 2 Mbps, with the resolution unchanged.

Although the structures of the devices are described in theabove-described embodiments, the respective devices may be constitutedby using the digital signal conversion method of the present inventionas software.

According to the present invention, decoding along with motioncompensation is carried out on an input information signal which iscompression-coded along with motion detection, and signal conversionprocessing is carried out on the decoded signal. On this convertedsignal, compression coding processing along with motion detection basedon motion vector information of the input information signal is carriedout. When resolution conversion processing is applied as this signalconversion processing, compression coding processing along with motioncompensation based on information obtained by scale-converting themotion vector information in accordance with the resolution conversionprocessing is carried out on the converted signal. Particularly, themotion vector information required at the time of compression coding isconverted in scale in accordance with the resolution conversion rate,and a narrow range is searched. Therefore, the calculation quantity atthe time of motion vector estimation can be significantly reduced, andminiaturization of the device and reduction in the conversion processingtime can be realized.

Also, according to the present invention, partial decoding is carriedout on an input information signal on which compression coding includingpredictive coding along with motion detection and orthogonal transformcoding is performed, and a decoded signal of the orthogonal transformdomain is thus obtained. Then, signal conversion processing is carriedout on the decoded signal of the orthogonal transform domain. On thisconverted signal, compression coding processing along with motioncompensation prediction using motion detection based on motion vectorinformation of the input information signal is carried out. Whenresolution conversion processing is applied as this signal conversionprocessing, compression coding processing along with motion compensationbased on information obtained by converting the motion vectorinformation in accordance with the activity obtained from the resolutionconversion processing is carried out on the converted signal. Therefore,the motion vector information required at the time of compression codingcan be estimated by searching a narrow range, and the calculationquantity can be significantly reduced. Thus, miniaturization of thedevice and reduction in the conversion processing time can be realized.Also, since signal conversion processing can be carried out in theorthogonal transform domain, inverse orthogonal transform processing isnot required and decoding (inverse orthogonal transform) to the timedomain or spatial domain is not required. Therefore, the calculation issimplified and conversion of high quality with less computational errorscan be carried out.

Moreover, according to the present invention, partial decoding iscarried out on an input information signal on which compression codingincluding predictive coding along with motion detection and orthogonaltransform coding is performed, and a decoded signal of the orthogonaltransform domain is thus obtained. Then, signal conversion processing iscarried out on the decoded signal of the orthogonal transform domain. Onthis converted signal, compression coding processing is carried out byadding motion vector information converted on the basis of motion vectorinformation of the input information signal. Therefore, when resolutionconversion processing is applied as this signal conversion processing,compression coding processing by adding information obtained byscale-converting the motion vector information in accordance with theresolution conversion processing is carried out on the converted signal.

That is, since the motion vector information added at the time ofcompression coding can be estimated by searching a narrow range, and thecalculation quantity at the time of motion vector estimation can besignificantly reduced. Also, since signal conversion processing can becarried out in the orthogonal transform domain, inverse orthogonaltransform processing is not required. In addition, since motioncompensation processing is not used at the time of decoding and coding,the calculation quantity can be reduced further.

1. A digital signal conversion method comprising: an inverse orthogonaltransform step of carrying out inverse orthogonal transform on anintra-frame coded signal and a forward predictive coded signal, of adigital signal of a first format including an intra-frame coded signalprocessed by intra-frame coding and a forward predictive coded signaland a bidirectionally predictive coded signal processed by forward andbidirection inter-frame predictive coding along with motion detection; amotion compensation out put generation step of generating a motioncompensation output to be added to the partially decoded forwardedpredictive coded signal and bidirectionally predictive coded signal onthe basis of the conversion output from the inverse orthogonal transformstep; an orthogonal transform step of orthogonally transforming themotion compensation output from the motion compensation outputgeneration step; an addition step of adding the orthogonal transformoutput from the orthogonal transform step to the partially decodedforward predictive coded signal and bidirectionally predictive codedsignal; a conversion step of carrying out signal conversion processingon the addition output between the addition step and the coding step,wherein at the coding step, the compression coding processing is carriedout on the converted signal from the conversion step; and a coding stepof carrying out compression coding on a signal based on the additionoutput and outputting a digital signal of a second format, wherein atthe conversion step, signal conversion is carried out on the output fromthe addition step by using a transform matrix generated on the basis ofan inverse orthogonal transform matrix corresponding to an orthogonaltransform matrix used for orthogonal transform coding performed on thedigital signal of the first format and an orthogonal transform matrixcorresponding to an inverse orthogonal transform matrix used forobtaining the digital signal of the second format.